Pauson-khand reaction of allenic hydrocarbons: Synthesis of 4-alkylidenecyclopentenones

Article abstract of DOI:10.1002/ejoc.200901224

The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4-alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio- and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, whi

Full text of DOI:10.1002/ejoc.200901224

FULL PAPER
DOI: 10.1002/ejoc.200901224
Pauson–Khand Reaction of Allenic Hydrocarbons: Synthesis of
4-Alkylidenecyclopentenones
Frédéric Antras,[a] Stéphane Laurent,[a] Mohammed Ahmar,[a] Henry Chermette,[b] and
Bernard Cazes*[a]
Keywords: Allenes / Cycloaddition / Enones / Configuration determination / Density functional calculations
The carbonyldicobalt-mediated alkyne/allene/CO cocycliza-
tion gives 4-alkylidenecyclopentenones as the major [2+2+1]
cycloadducts. The regio- and stereoselectivities depend
mainly on the substitution pattern of both the alkyne and the
allenic moieties, which can be rationalized using the Magnus
ment with more recent mechanistic studies, our results pro-
vide evidence that both initial pseudo-equatorial and
pseudo-axial coordination modes of the allenic hydrocarbons
onto one of the cobalt atoms of the primary alkyne–dicobalt
complex are involved. DFT calculations supporting both
mechanism. However, contrary to this model, and in agree- these coordination modes are given.
Introduction
The Pauson–Khand Reaction (PKR), a formal [2+2+1]
cycloaddition, first described and used over three decades
ago, is a carbonyldicobalt-mediated carbonylative cocycli-
zation of an alkyne with an alkene giving cyclopentenones
(Scheme 1).[1,2] The main feature of this cycloaddition is its
high sensitivity to steric hindrance, so that the major re-
gioisomeric cyclopentenone obtained is the one with the
more bulky R and R1 groups of both unsaturated partners
at the α- and αЈ-positions of the cyclopentenone keto group
(Scheme 1). However, the PKR with linear and cyclic alk-
enes was shown to be a low-yielding cycloaddition.[3] Con-
sequently, the intermolecular PKR was initially limited to
Scheme 1. Pauson–Khand reaction (PKR).
Major improvements in the PKR came from finding new
strained olefins such as norbornene,[1,4] norbornadiene,[4a] energetically activated procedures[15] or by using milder
and 7-oxanorbornene derivatives.[5] It was later extended to conditions with various promoters such as silica,[16]
a few other classes of unsaturated compounds, such as: cy- amines,[17] dimethylsulfoxide (DMSO),[18] sulfides[19] and
clobutenes,[6] allenes,[7] methylenecyclopropanes,[8] or cyclo- molecular sieves.[20] Particularly, the use of tertiary amine
propenes,[9] and to some heteroatom-substituted[10] or acti- N-oxides allowed the reaction to be carried out at room
vated alkenes.[11] On the other hand, the carbonylative cy- temperature.[21] Recent other developments in this powerful
cloaddition of ene-ynes turned out to be far more efficient methodology includes the possibility of performing the cy-
and synthetically useful.[12,2] Thus, intramolecular PKR has cloaddition under catalytic conditions[22] or enantioselec-
emerged as one of the most powerful routes to five-mem- tively.[23] It is noteworthy that similar intramolecular [2+2+1]
bered ring systems and has become the key step in numer- cycloadditions have been recently described as being cata-
ous syntheses of complex polycyclic cyclopentenones[13] and lyzed by several other transition-metal complexes (Ti, Mo,
natural products.[14]
Fe, Ru, Rh, Ir, and Pd).[24] However, the Co2(CO)8-medi-
ated PKR remains very useful because of its specific stereo-
chemical features and because of its high chemical compati-
bility with numerous functionalities.
A mechanistic rationalization for the PKR was first pro-
posed in 1985 by Magnus.[25] This was later revisited by
Laschat who shed new light on the coordination step in
which the alkene coordinates to one of the cobalt atoms of
the initial alkyne–dicobalt complex 2.[26] Moreover, theoret-
[a] Université Lyon 1, CNRS UMR 5246-ICBMS, Laboratoire
COSMO, Bât. Curien,
43 Bd du 11 Novembre 1918, 69622 Villeurbanne, France
[b] Université Lyon 1, Laboratoire de Chimie-Physique Théorique,
CNRS UMR 5180 Sciences Analytiques, Bât. Dirac,
43 Bd. du 11 Novembre 1918, 69622 Villeurbanne, France
E-mail: cazes@univ-lyon1.fr
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Pauson–Khand Reaction of Allenic Hydrocarbons
ical studies[27] (DFT calculations of the acetylene or pro- into the PKR with allene 3a and allenic hydrocarbons 3,
pyne/ethylene/CO cocyclizations) and ESI tandem MS ex- which gave 4-alkylidenecyclopentenones 4 with high selec-
periments,[28] confirmed the successive steps of the overall tivity in most cases.
reaction. However, the Co2(CO)8-mediated reaction of 1,n-
enynes has sometimes led to unexpected unsaturated (keto)
compounds or other by-products, which also brought some
light to the different steps of the PKR mechanism.[29]
At the outset of our work,[7a] additional data on the reac-
tivity of allenic structures within PKR-like reactions were
available. Octacarbonyldicobalt was shown to polymerize
allene,[30] and Pauson’s group was unable to characterize
any cycloadduct from the reaction of cyclonona-1,2-diene
under thermal conditions.[2k] Aumann realized the first
intermolecular Fe2(CO)9-mediated alkyne/allene/CO cocy-
clization, but 4-alkylidenecyclopentenones were obtained
with poor selectivities along with cyclopentadienones and
cyclopentadienone–iron complexes.[31] Likewise, the first
iron-mediated intramolecular cycloaddition of 1,6-yne-all-
enes was described.[32] Since then, the intramolecular PKR
of 1,n-yne-allenes giving bicyclic cyclopentenones has also
Scheme 2. Pauson–Khand reaction of allenic hydrocarbons 3.
[33]
been described as being mediated by Co2(CO)8
or
Mo5(CO)6,[34] and was further developed using rhodium ca-
talysis.[35,36]
Results and Discussion
In this context, we became interested in the reactivity
of allenic compounds 3 under mild conditions within the
intermolecular Pauson–Khand reaction (Scheme 2).[7] In-
deed, because of the two orthogonal double bonds of the
Model PKR of Alkynes with Allenes
Exploratory experiments with the acetylene–dicobalt
allenic unit, the study of the alkyne/allene/CO cocyclization complex 2a (R = RЈ = H) appeared to be complicated. So,
was expected to bring up interesting results in several direc- as a starting point, the reaction of a symmetrically disubsti-
tions: (1) the possibility of achieving a short route to the tuted alkyne–dicobalt complex such as 4-octyne–dicobalt
well-known 5-alkylidenecyclopentenones 6,[37] or to the complex 2b with a monoalkylallene (e.g., 1,2-nonadiene 3b)
otherwise difficult to prepare, 4-alkylidenecyclopentenones was taken to be an appropriate PKR model that could be
4 and 5;[38] (2) the opportunity to gain new insights into the used to check the feasibility of the cycloaddition and to
PKR mechanistic pathway by observing the selectivity of find optimum reaction conditions. Indeed, the carbonyl–di-
the reaction leading to cyclopentenones 4–6 (Scheme 2). cobalt complex 2b, generated from 4-octyne (1b) in almost
Thus, we report herein a full account of our investigations quantitative yield, reacted easily with one equivalent of 1,2-
Table 1. Model Pauson–Khand reaction with allenic hydrocarbons 3b.
Entry
Allene 3b
[n equiv.]
Promoter
Yield [%][a]
4bb + 5bb
Ratio[b]
4bb/5bb
1
2
3
4
5
6
7
1
NMO (6 equiv.)
NMO (6 equiv.)
NMO (6 equiv.)
NMO (6 equiv.)
TMANO (6 equiv.)
TMANO·H2O
59
96:4
96:4
96:4
96:4
95:5
95:5
94:6
1 + 0.5
1.2
1.5
1.5
1.5
(61)
(63)
71
(68)
(32)
(15)
1.5
CAN (6 equiv.)
[a] Yields of isolated product after flash chromatography. Those in brackets were GC yields (internal standard: octadecane). [b] Ratio
4bb/5bb was determined by GC analysis of the crude product.
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FULL PAPER
nonadiene (3b) under Schreiber’s conditions[21] in dichloro- Procedure B, but the reaction mixture was stirred for 2 h
methane at 0–20 °C, in the presence of six equivalents of N- at –78 °C before warming up slowly from –78 °C to room
methylmorpholine oxide (NMO; Table 1). 4-Heptylidenecy- temperature over 2 h, and stirring for a further 2 h at this
clopentenone [(E)-4bb] was obtained with high regioselec- temperature. Cyclopentenones 4bb and 5bb were then ob-
tivity, along with traces of the regioisomeric cyclopentenone tained in 77% combined yield with a similar 97:3 regioselec-
5bb, in a combined yield of 59% (4/5 ratio 96:4, Table 1, tivity (entry 3). Procedures A–C were all performed on a 1–
entry 1). The yield of 4bb and 5bb was increased when a 5 millimolar scale and the study culminated in 81% yield
slight excess of 1,2-nonadiene (3b) was used (entries 2–4). for Procedure B. However, all these procedures were less
This study resulted in an initial optimized procedure (Pro- efficient (25–35% yields) when carried out on a preparative
cedure A), where dichloromethane was used as solvent with 20–50 mmol scale, presumably because of the necessary de-
1.5 equiv. of allene 3b (entry 4); under these conditions, cy- crease in the relative volume of solvent used.
clopentenones 4bb and 5bb were obtained in 71% overall
For this purpose, a further set of conditions was estab-
yield.[7a] Other promoters were also tested: Trimethylamine lished (Procedure D) that resulted in an optimized 50%
oxide (TMANO) gave similar results (entry 5), whereas its yield (entry 4). This method involved the slow addition at
hydrate TMANO·H2O (entry 6), and cerium ammonium ni- –40 °C of the promoter NMO, which was diluted in dichlo-
trate (CAN; entry 7) were less efficient in promoting the romethane, then allowing the reaction to come to room
cycloaddition.
temperature over 1 h, then stirring again for 2–5 h. With
The possibility of using gaseous allene 3a (b.p. –33 °C) experimental procedures A–D in hand, we then looked at
as an unsaturated partner prompted us to carry out the the scope and limitations of the PKR with allenic hydro-
reaction at low temperature. Another parameter was the na- carbons 3. We were particularly interested in the relation-
ture of the solvent(s) since it has been previously demon- ship between the selectivities obtained in the formation of
strated that the use of tetrahydrofuran (THF) as a cosolvent cyclopentenones 4–6 and the substitution patterns of both
increases both the reaction rate and the yield of PKRs.[39] the acetylenic and allenic partners.
Thus, the effects of these parameters on the yield and selec-
tivities of our model PKR (2b + 3b) were investigated.
When the cycloaddition was carried out in CH2Cl2/THF
(1:1) at –78 °C, the reaction did occur but was very slow, as
PKRs of Disubstituted Alkynes with Allenes
shown by GLC analysis of the reaction mixture (analysis
The reactivities of symmetrical dialkylalkyne–dicobalt
performed every two hours); after 8 h, cyclopentenone (E)- complexes 2b–d with allene 3a and a range of monosubsti-
4bb was then isolated in 20% yield, with most of the 1,2- tuted allenes 3b–d were first studied. The results are sum-
nonadiene (3b) being recovered unchanged. Warming up marized in Table 3. All reactions gave cyclopentenone (E)-
the reaction mixture from –78 °C to room temperature re- 4 with high regio- and stereoselectivities under procedures
sulted in a set of further experimental conditions (Pro- A, B and D. Procedure B, when carried out in a CH2Cl2/
cedures B–C), which are summarized in Table 2.
THF mixture, gave higher yields (compare entries 1/2, 4/5,
8/9, and 11/12), and up to 91% yield of cyclopentenones
4db and 5db (entry 7). Variation of the solvent and tempera-
ture had no effect on these selectivities, which seemed to
depend only on the steric hindrance of the alkyne substitu-
ent R. Indeed, for the reactions of complexes 2b–d with
allene 3b, both the regioselectivity (4/5) and the stereoselec-
tivity [(E/Z)-4] were higher when the R group was more
bulky (compare entries 4–6 with entry 7). Allenic hydro-
carbons 3c and 3d with a larger R1 group (R1 = Ph or
SiMe3) gave cyclopentenones (E)-4bc and (E)-4bd as single
products (entries 8–12). As mentioned above, procedure B
was less efficient on a preparative scale (20–50 mmol) and
furnished cyclopentenones 4da and 4bc in modest 25% and
36% yields, respectively (entries 3 and 10). Cyclopentenone
4cb can be obtained by Procedure D in 53% yield on a
40 mmol scale (entry 6). It should also be noted that, on
such preparative 30–40 mmol scales, it was possible to iso-
late small amounts (ca. 1–3%) of cyclopentene-1,3-dione 7,
Table 2. Procedures A–D.
[a]
Entry
Solvent
(ratio)
T
[°C]
Time
[h]
Yield [%][c] Ratio[d,e]
4bb + 5bb 4bb/5bb
1
2
A
B
CH2Cl2
0–20
15–18
71
81
96:4
95:5
CH2Cl2/THF –78 to r.t.[f]
1
3
4
2
1
(1:1)
CH2Cl2/THF –78 to r.t.[g]
(1:1) then r.t
D[b] CH2Cl2/THF –40 to r.t.
(1:1) then r.t
then r.t.
3
4
C
77
50
97:3
94:6
[a] Procedures A–C were performed on a 1–10 mmol scale (2b/3b/
NMO, 1:1.5:6). [b] Procedure D was performed on a 20 mmol scale.
[c] Yield of isolated products analyzed by flash chromatography.
[d] Obtained by GC analysis of the crude reaction product. [e] If
necessary, the less polar cyclopentenone 5bb can be easily separated
from 4bb by flash chromatography. [f] –78 °C to r.t. over 1 h. [g]
Stirring 2 h at –78 °C, then warming to r.t. over 2 h and stirring
for a further 2 h at r.t.
In Procedure B, the NMO promoter was added as a solid resulting from the cobalt-catalyzed oxidative cleavage of the
at –78 °C over a few minutes. The reaction mixture was then exocyclic double bond of the cyclopentenone 4 [1,3-diones
warmed to room temperature over 1 h and stirred for 3 h at 7d (Table 3, entry 3) and 7c (Table 4, entry 2)].[40]
room temperature before workup; under these conditions,
We then examined the PKRs of a symmetrical dialkylalk-
cyclopentenones 4bb and 5bb were obtained in 81% com- yne such as 4-octyne (1b; R = nC3H7) with several polysub-
bined yield (Table 2, entry 2). Procedure C was similar to stituted allenes 3e–j under experimental procedures A, B or
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Pauson–Khand Reaction of Allenic Hydrocarbons
Table 3. Pauson–Khand reaction of symmetrical dialkylalkynes with monosubstituted allenes.
Entry
2b–d
Allene
3a–d
Procedure[a]
Cyclopentenones
Yield [%][c]
4 + 5
Ratio
4 (E/Z)[e]
Yield [%][c]
4–5
4/5[d]
7
1
2
3
4
5
6
7
8
2d
2d
2d
2b
2b
2c
2d
2b
2b
2b
2b
2b
R = CH3
R = CH3
R = CH3
3a
3a
3a
3b
3b
3b
3b
3c
3c
3c
3d
3d
R1 = H
A
B
4da
4da
4da
59
62
25
71
81
53
91
33
70
36
40
61
–
–
–
96:4
95:5
97:3
–
–
–
R1 = H
R1 = H
B[b]
A
1.5
R = nC3H7
R = nC3H7
R = nC2H5
R = CH3
R = nC3H7
R = nC3H7
R = nC3H7
R = nC3H7
R = nC3H7
R1 = nC6H13
R1 = nC6H13
R1 = nC6H13
R1 = nC6H13
R1 = Ph
4bb + 5bb
4bb + 5bb
4cb + 5cb
4db + 5db
4bc
100:0
100:0
97:3
94:6[f]
100:0
100:0
100:0
100:0
100:0
B
D
B[f]
A
89:11[f]
Ͼ 99:1
Ͼ 99:1
Ͼ 99:1
Ͼ 99:1
Ͼ 99:1
9
R1 = Ph
B
4bc
4bc
4bd
4bd
10
11
12
R1 = Ph
B[b]
A
R1 = SiMe3
R1 = SiMe3
B
[a] Procedure A: reaction carried out in CH2Cl2 at 0–20 °C. Procedure B: reaction carried out in CH2Cl2/THF (1:1), warming up from
–78 °C to r.t. over 1 h, then stirring at r.t. for 1–3 h. Procedure D (20–40 mmol scale): reaction carried out in CH2Cl2/THF (1:1) with
addition of a CH2Cl2 solution of NMO at –40 °C. [b] Reaction carried out on a 40 mmol scale. [c] Yield of isolated products after flash
chromatography. The less polar cyclopentenone 5 is easily separated from cyclopentenone 4. [d] Ratio of regioisomers 4/5 was obtained
by GC analysis of the crude reaction product. [e] Ratios E/Z of 4 were obtained from GC analysis of the crude reaction product. [f]
Reaction was carried out on a 11 mmol scale. Ratios 4/5 and E/Z (4) were obtained from isolated products.
D (Table 4) [one example was also studied with 3-hexyne 1c with the regioisomeric cyclopentenone 5, both of which
(R = Et): Table 4, entry 2]. The 1,1-disubstituted allenes 3e have the larger R group on the 2-position of the cyclopent-
and 3f gave the cyclopentenone 4be as the major adduct enone (Table 5). However, the dicobalt complexes 2i also
and 4ce and 4bf as single adducts (Table 4, entries 1–4). A afforded the alternative regioisomeric cyclopentenone (E)-
small amount (5%) of the regioisomeric cyclopentenone 5be 4Јib, with the larger n-butyl group on the 3-position of the
was also isolated in the cycloaddition of complex 2b with cyclopentenone (entry 1); complexes 2j and 2k did not give
3e (Table 4, entry 1). 1,3-Disubstituted allenes such as 6,7- the corresponding cyclopentenones 4Јjb and 4Јkb (entries 2
tridecadiene (3g) and cyclonona-1,2-diene (3h) gave cyclo- and 3). Thus, the bulky phenyl and tert-butyl groups of the
pentenones (E)-4bg and 4bh, respectively, in fair 66–81% 2-alkyne–dicobalt complexes 2j–k completely controlled the
yields (entries 5–7). 2-Methyl-2,3-decadiene (3i) was studied selectivity of the cycloaddition to cyclopentenones 4jb and
as an example of a trisubstituted allene (entry 8); in this 4kb. It is noteworthy that the regioselectivity is lower (4kb/
case the reaction gave a 60:40 mixture of cyclopentenones 5kb = 88–92:12–8) when a small group, such as methyl, is
4bi and (E)-5bi in a lower overall yield (41%). No reaction one of the alkyne substituents; this regioselectivity was also
was observed with tetrasubstituted allenes such as tetra- observed for the reaction with the 2-butyne–dicobalt com-
methylallene (3j) under procedures A or B (entry 9). These plex 2d (Table 3, entry 7: 4db/5db = 89:11).
last reactions clearly show that the PKR of allenic com-
pounds is also very sensitive to steric hindrance around the
allenic unit. It is noteworthy to point out here that the reac-
tion of vinylidenecyclohexane (3f) did not give any 5,5-di-
PKRs of Monosubstituted Alkynes with Allenes
substituted cyclopentenone 5bf, whereas allenes 3e and 3i,
The cycloaddition of monosubstituted alkynes (1-alkynes
which have a dimethyl-substituted terminal carbon, led to 2e–g) with allenes 3a–d were examined under procedure A
the 5,5-disubstituted cyclopentenones 5be and 5bi, respec- or B (Table 6). First, the cycloaddition of 1-pentyne (2e)
tively, as minor cycloadducts (compare entries 3 and 4 with with allene (3a) gave cyclopentenone 4ea in 60% yield
entries 1 and 8). This might be a result of the more sterically (Table 6, entry 1). All other reactions tested gave cyclopent-
demanding environment about the cyclohexane ring of enone 4 (mixture of E and Z isomers) as the major cyclo-
vinylidenecyclohexane (3f), compared to that of 1,1-dimeth- adducts, along with the regioisomeric cyclopentenone 5 (en-
ylallene (3e).
tries 2–8), except for the reactions with trimethylsilylallene
We also studied the reactivities of a few disymmetrical 3d, which did not give the corresponding cyclopentenones
alkynes, such as 2-alkynes 1i–k (RЈ = CH3) with 1,2-nona- 5ed and 5fd (entries 9–10). The regioselectivities 4/5 (ap-
diene (3b) under procedure B (Table 5). All these reactions proximately 83–92:17–8) were lower than for the cyclo-
gave the cyclopentenone (E)-4 as the major product along addition of dialkylalkynes 2b and 2c (Table 3, entries 4–6)
Eur. J. Org. Chem. 2010, 3312–3336
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F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
Table 4. PKR of symmetrical alkynes with polysubstituted allenes.
[a] Procedure A: reaction carried out in CH2Cl2 at 0–20 °C. Procedure B: reaction carried out in CH2Cl2/THF (1:1), warming up from
–78 °C to r.t. over 1 h, then stirring at r.t. for 1–3 h. [b] Yields of isolated product after flash chromatography. [c] Cyclopentenones 4bi
and 5bi were separated as individual regioisomers by flash chromatography. [d] Reaction carried out with the 3-hexyne dicobalt complex
2c (R = Et). [e] n.r.: no reaction.
Table 5. PKR of disymmetrical alkynes.
Entry
1
Alkyne–[Co] 2i–k[a]
2i R = nC3H7
Product 4, 4Ј and 5
Yield 4 + 5 (+ 4Ј)[b]
Ratio 4/5[c]
Ratio E/Z-4[c]
4ib + 5ib
+ 4Јib
4jb + 5jb
4kb + 5kb
70
14
85
61
88:12
Ͼ 99:1
Ͼ 99:1
93:7
2
3
2j R = Ph
2k R = tBu
85:15
92:8
Ͼ 99:1
[a] [Co] = Co2(CO)6. [b] Yields of isolated product by flash chromatography. [c] Ratios 4/5 were obtained from GC analysis of the crude
reaction product.
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Pauson–Khand Reaction of Allenic Hydrocarbons
Table 6. PKR of monosubstituted alkynes with allenes 3a–d.
[a] Yield of isolated products after flash chromatography. [b] Ratio 4/5 was obtained from GC analysis of the crude reaction product. [c]
1
Ratios E/Z for cyclopentenones 4 were obtained from GC analysis and/or from H NMR spectra.
and similar to those obtained with 2-alkynes 2d (Table 3, efficient. It is also worth mentioning that, similar to the
entry 7) and 2i–k (Table 5). These cycloadditions were less reaction of vinylidenecyclohexane (3f) with complex 2b
stereoselective because cyclopentenones (Z)-4 were ob-
tained in larger amounts (E/Z = 70–75:30–25; entries 2–8).
Here again, it is worth mentioning the different behavior of
trimethylsilylallene (3d), the cycloadditions of which were
more stereoselective (compare entries 9 and 10 with entries
2–8). This demonstrates the importance of the steric effect
of the allenic substituent on both the regio- and stereoselec-
tivities of the cycloaddition.
The reactivity of vinylidenecyclohexane (3f), a 1,1-disub-
stituted allene, was also studied (Scheme 3). Both pro-
cedures A and B gave 4-alkylidenecyclopentenones 4hf (R
= nC5H11) and 4ff (R = Ph), from 2h and 2f, respectively,
with complete regioselectivity. Here again, procedure B,
where the reaction is performed in CH2Cl2/THF, was more (3f).
Scheme 3. PKR of 1-alkynes 2h and 2f with vinylidenecyclohexane
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F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
(Table 4, entries 3 and 4), no 5,5-disubstituted cyclo-
pentenone (5hf or 5ff) was isolated.
PKRs of Acetylene with Allenes
The reaction of acetylene hexacarbonyldicobalt complex
2a with 1,2-nonadiene (3b) appeared to be more complex
than the cycloadditions of mono- and disubstituted alkynes
2b–k. When the conditions described for procedure B were
applied for 15 h, the reaction gave a complex mixture of
four cyclopentenones: the 4-alkylidenecyclopentenones 4ab
(E+Z), 5ab, and the 5-alkylidenecyclopentenone (E)-6ab in
a 73:7:20 ratio, together with a tricyclic diketone 10b, which
was isolated in 11% yield (Table 7, entry 1).
The structure of the latter diketone 10b was determined
by analysis of 2D NMR analysis (COSY experiments). This
by-product 10b might arise from the unstable isomeric cy-
clopentadienone 7ab, which would be slowly generated in
situ by the N-methylmorpholine-catalyzed isomerization of
the primary cyclopentenones 4ab. The [4+2] dimerization
of cyclopentadienone 7ab would then give the diketone
10b.[41] A plausible alternative pathway might involve the
three-step sequence: (1) the isomerization of cyclo-
pentenone 4ab to cyclopentadienone 7ab, (2) the Diels–
Alder reaction of this intermediate cyclopentadienone 7ab
with cyclopentenone 4ab, leading to the bicyclic diketone
Scheme 4. Plausible pathways to [4+2] dimers 10 and 11.
8b,[42] and (3) the isomerization of this cycloadduct 8b to allowed to slowly warm from –78 °C to room temperature
cyclopentenone 10b (Scheme 4). It is noteworthy that the over 4 h, the amount of regioisomer 5ab formed decreased,
isomeric cyclopentenone-dimer 11b could not be detected.
while the amount of 5-alkylidenecyclopentenone (E)-6ab in-
The reaction times of further cycloadditions were then creased (compare entries 3 and 4). The E/Z selectivities for
shortened in an attempt to avoid the isomerization of 4ab cyclopentenones 4ab appeared to remain relatively un-
to cyclopentadienone 7ab; as hoped, this prevented the for- changed. Reaction of dicobalt complex 2a with phenyl-
mation of the cyclopentenone 10b (Table 7, entries 2–4). allene 3c under procedure B also gave three isomeric cyclo-
The selectivities of the formation of the isomeric cyclo- pentenones 4–6ac (entry 5). Thus, the formation of the 5-
pentenones 4–6ab were found to depend upon the tempera- alkylidenecyclopentenone 6 seems to be specific to the reac-
ture. Particularly, under procedure C when the reaction was tivity of the acetylene–dicobalt complex (2a).
Table 7. Pauson–Khand reaction of acetylene.
E
ntry Allene
Procedure[a] T [°C]
Time
[h]
Cyclopentenones
4–6
Yield [%][d] Ratio[e]
4 + 5 + 6 4/5/6
E/Z Ratio[f] Yield [%][d]
3b–c
4
10b
1
2
3
4
5
3b
3b
3b
3b
3c
R1 = nC6H13
"
B[b]
A
B
–78 to r.t. (1 h)
0–20
–78 to r.t. (1 h)
–78 to r.t. (4 h)
–78 to r.t. (2 h)
2 + 15 (r.t.) 4ab + 5ab + 6ab
71
78
79
82
28
73:7:20
85:8:7
90:3:7
85:2:13
77:5:18
78:22
70:30
73:27
75:25
86:14
11
–
–
–
–
2
4ab + 5ab + 6ab
4ab + 5ab + 6ab
4ab + 5ab + 6ab
4ac + 5ac + 6ac
"
"
1 + 2 (r.t.)
4 + 2 (r.t.)
2 + 2 (r.t.)
C
R1 = Ph
B[c]
[a] Procedure A: reaction carried out in CH2Cl2 at 0–20 °C. Procedure B: reaction carried out in CH2Cl2/THF (1:1), warming up from
–78 °C to r.t. over 1 h, then stirring at r.t. for 1–3 h. Procedure C: warming up from –78 °C to r.t. over 4 h, then stirring at r.t. for 2 h.
[b] Procedure B, but stirring at r.t. overnight (15 h). [c] Reaction performed on a 17 mmol scale. [d] Yield of isolated product after flash
chromatography. [e] Ratios of regioisomers 4/5/6 were obtained from GC analysis of the crude reaction product. [f] Ratios E/Z of
cyclopentenones 4 were obtained from GC analysis of the crude reaction product.
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Pauson–Khand Reaction of Allenic Hydrocarbons
Results for the cycloadditions of 2a with vinylidenecyclo- namely 10a and 11a, were obtained in 22% and 7% yields,
hexane (3f) are summarized in Table 8. All the reactions respectively (Scheme 6). All attempts to isolate 4-methylene-
gave mixtures of cyclopentenone 4af and 5-cyclohexylidene- cyclopentenone (4aa) by carrying out the reaction at –78 °C
cyclopentenone (6af) regardless of which procedure was without warming, failed, and the reaction gave only mix-
used (entries 1–3). Formation of the 5,5-disubstituted cyclo- tures of dimers 10a and 11a. The formation of these dimers
pentenone 5af was not observed, whereas the amount of might be rationalized as for the formation of adduct 10b
cyclopentenone 6af increased up to 28 molar% when the (Scheme 4).
reaction was carried out at lower temperature (entry 3).
Table 8. Pauson–Khand reaction of acetylene 1a with 3f.
Structure and Stereochemistry Assignments of 4- and 5-
Alkylidenecyclopentenones
The structure and stereochemistry of alkylidenecyclo-
pentenones 4–6 were assigned by means of their 1H and 13
C
NMR spectra. Thus, an 4-alkylidenecyclopentenone struc-
ture such as the cyclopentenone (E)-4bb was easily distin-
guished from the possible 5-alkylidenecyclopentenone
structure 6bb.[38] Indeed, the α-keto methylene group (C-5)
Entry Reaction
conditions
Yields[%][a]
4af + 6af
Ratio
4/6[b]
1
H2 of the former gave rise to an upfield H NMR signal at
δ = 2.86 ppm, whereas the signal from the (C-4)H2 group
of a typical 5-alkylidenecyclopentenone structure, such as
(E)-6bm (R1 = nC5H11), was found downfield at δ =
3.02 ppm [δ = 3.00 ppm for (Z)-6bm],[43] or at δ = 3.19 ppm
for cyclopentenone (E)-6ab (Figure 1). The chemical shifts
of their exocyclic vinylic protons are also very distinctive.
These proton NMR signals are shifted upfield at δ = 5.5–
5.9 ppm for 4-alkylidenecyclopentenones 4 [δ = 5.75 ppm
for (E)-4bb] and downfield (Ն6 ppm) for the 5-alkylidene-
cyclopentenone structure [δ = 6.57 ppm and 5.96 ppm for
cyclopentenones (E)- and (Z)-6bm (R1 = nC5H11), respec-
tively].[43]
1
2
3
20 °C
51
52
64
96:4
80:20
72:28
Procedure B (–78 °C to r.t. over 1 h)
Procedure C (–78 °C to r.t. over 4 h)
[a] Yields (4af + 6af) of isolated products after flash chromatog-
raphy. [b] Ratios 4af/6af were obtained from GC analysis of the
crude reaction product.
When the reactivity of cyclonona-1,2-diene (3h), as an
example of a 1,3-disubstituted allene was examined under
the conditions described for procedure C, the bicyclic cyclo-
pentenone 4ah was obtained as a single adduct in 59% yield
(Scheme 5); no isomeric 5-alkylidenecyclopentenone-type
product 6ah was detected.
Scheme 5. Pauson–Khand reaction of acetylene (2a) with cy-
clonona-1,2-diene (3h).
Finally, attention was directed towards the cycloaddition
of acetylene (1a) with allene (3a). Whereas no 4-methylene-
cyclopentenone (4aa) was obtained, instead, two regioiso-
meric [4+2] dimers of 3-methylcyclopentadienone 7aa,
Figure 1. Structure assignment of alkylidenecyclopentenones 4 and
6.
The E/Z configurational assignment of the exocyclic
double bond of stereoisomers (E)-4 and (Z)-4 can be deter-
mined by using nuclear Overhauser effect (NOE) NMR
spectroscopy.[44,45] As an example, the (E)-configuration of
cyclopentenone 4bb was proved by irradiating the exocyclic
vinylic proton at δ = 5.75 ppm; this resulted in the enhance-
ments (5–6% NOE) of both allylic methylene groups at δ
Scheme 6. Pauson–Khand reaction of acetylene with allene.
Eur. J. Org. Chem. 2010, 3312–3336
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F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
= 2.14 and 2.45 ppm. Likewise, irradiation of the αЈ-keto cause it experiences a low-field shift due to the magnetic
methylene group at δ = 2.86 ppm gave an effect (5% NOE) anisotropy of the (C-2)=(C-3) double bond [H-cis appears
only on the allylic protons at δ = 2.14 ppm (Figure 1).
at δ = 5.67 ppm in (E)-4eb and H-trans at δ = 5.55 ppm in
However, the easiest and least ambiguous way to assign (Z)-4eb].
the (E) or (Z)-configuration of these 4-alkylidenecyclo-
pentenones 4 relies on comparisons between the chemical
shifts of both C-3 and C-5 carbons of each isomer (Fig-
ure 2). Thus, the C-5 carbon nucleus of cyclopentenone (E)-
4 resonates at high-field (δ = 37–39 ppm) compared to the
analogous carbon of the (Z)-4 isomer (δ = 40–43 ppm) be-
cause of the shielding due to a positive cis-γ-effect (γ-com-
pression effect) from the allylic carbon (C-4)=C–CH2 at δ
= 30–31 ppm [δ = 37.3 ppm for (E)-4cb and 42.8 ppm for
(Z)-4cb].[45,46] A similar shielding effect is observed for the
C-3 carbon in cyclopentenone (Z)-4, which resonates at
higher field [δ =167.7 ppm for (Z)-4cb], whereas it is further
downfield for the isomer (E)-4 [δ =168.2 ppm for (E)-4cb].
This last shielding effect is stronger (by approximately
5 ppm) for the C-3 carbon of 3-unsubstituted cyclopen-
tenones (Z)-4 (RЈ = H). Thus, the C-3 carbon resonates
further upfield at δ = 149.3 ppm for (Z)-4eb, whereas it is
shifted more downfield (δ = 154.3 ppm) for the (E)-4eb iso-
mer (Figure 2).
Figure 3. Configurational assignment of the exocyclic double bond
of 4-alkylidenecyclopentenones (E)- and (Z)-4eb using 1H NMR
spectroscopy.
A further way to identify the stereoisomers of cyclo-
4
pentenones 4 rests on the allylic coupling constant J be-
tween the vinylic proton (C4)=CH and the (C-5)H2 methyl-
ene group. This constant has previously been demonstrated
to be higher for the vinylic proton H-cis that is transoid
with respect to the methylene group than for the corre-
sponding cisoid (H-trans): i.e., |4Jtransoid| Ͼ |4Jcisoid|.[44,48] In
the case of cyclopentenone 4eb, the H-cis vinylic proton of
(E)-4eb appears as an almost completely resolved triplet of
triplets at δ = 5.67 ppm (3J = 7.8 Hz and |4Jtransoid| =
1.7 Hz) whereas the H-trans proton of the isomer (Z)-4eb
resonates at δ = 5.55 ppm as a less well resolved triplet of
3
triplets with J = 7.5 Hz and |4Jcisoid| ≈ 0.7 Hz (Figure 3).
Simultaneously, the methylenic protons (C-5)H2 of isomer
(E)-4eb resonate upfield at δ = 2.96 ppm as a doublet
(|4Jtransoid| = 1.7 Hz), whereas they give a less well resolved
doublet downfield at δ = 2.91 ppm (|4Jcisoid| ≈ 0.7 Hz) for
the isomer (Z)-4eb. However, these vinylic and methylenic
protons often appear only as broad triplets and singlets be-
cause of several other long-range 5J and 6J couplings
4
through the dienic structure. Consequently, these J allylic
coupling constants are not always available and their use as
stereochemical proofs is thus restricted for cyclopentenones
4; moreover, their erroneous use may lead to incorrect
stereochemical assignments.[48,49]
Figure 2. Configurational assignment of the exocyclic double bond
of 4-alkylidenecyclopentenones (E)- and (Z)-4 using 13C NMR
spectroscopy.
Mechanism
Alternatively, the stereochemistry of the 3-unsubstituted
A comprehensive view of the different pathways possible
cyclopentenones 4 obtained from the PKRs of 1-alkynes for the PKRs of allenic hydrocarbons should rationalize the
1e–m (RЈ = H) could also be deduced from the chemical various regio- and stereoselectivities observed in the forma-
shifts of the vinylic protons H-3 and (C-4)=CH. Indeed, in tion of alkylidenecyclopentenones 4–6; a reasonable expla-
agreement with the Cárdenas rule,[47] the H-3 proton reso- nation must surely take into account both the steric features
nates at high-field for the (E)-4 isomer, whereas it is further of the allenic unit and the PKR Magnus mechanism de-
downfield for the (Z)-4 isomer because of a steric deshield- picted in Scheme 7.[25] This mechanistic model includes sev-
ing (∆δ ≈ 0.3–0.4 ppm) effect from the cis group R1 (Fig- eral steps from the tetrahedral alkyne–dicobalt cluster 2,
ure 3; the reference for the cis–trans description is the intra- which is initially formed from alkyne 1 and Co2(CO)8 (step
cyclic double bond). For the exocyclic vinylic proton (C- 1), and is the only isolable and well characterized intermedi-
4)=CH, the H-cis proton of the (E)-4 isomer is deshielded ate along the overall cycloaddition process.[50] This first step
compared with the H-trans proton of the (Z)-4 isomer, be- is assumed to be followed by the loss of a CO ligand from
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Pauson–Khand Reaction of Allenic Hydrocarbons
one of the cobalt atoms of cluster 2, leading to the coordi- cussed by Laschat who proposed a more realistic pseudo-
natively unsaturated alkyne–pentacarbonyldicobalt inter- axial coordination of the double bond because of the steric
mediate I (step 2). For NMO-promoted PKRs, this CO de- requirements of the methylene bridge of these compounds
coordination is clearly executed through its oxidation to (step 3, giving the intermediate II-ps-ax).[26] Finally, DFT
CO2 with concomitant formation of N-methylmorph- calculations on the propyne/ethylene PKR gave a more ac-
oline.[21] Further steps include: (1) olefin coordination to curate description of the cycloaddition(s) pathway(s) and
cobalt, which, for steric reasons, should preferentially take concluded that both olefin coordination modes were pos-
place anti to the larger substituent R of the alkyne in a sible.[27c,27f] It is worth mentioning that electronic factors
pseudo-equatorial position (ps-eq) with respect to the Co– may play an important role in the regioselectivity of the
Co bond (step 3); (2) alkene insertion into the formal RЈC– PKRs when electron-poor alkynes are involved (e.g., R =
Co bond giving the cobaltacycle III (step 4); (3) CO inser- CO2Et).[54,27f] However, it was shown that when both steric
tion into the R1C–Co bond giving the acylcobalt complex and electronic factors were considered, steric factors super-
IV (step 5); (4) reductive elimination creating the RC– seded the latter.
C(=O) bond of the intermediate V (step 6), and (5) decom-
Such electronic factors were also encountered in the
plexation of the final cyclopentenone from the Co2Ln clus- PKRs of trimethylsilylalkynes with allenic hydrocarbons
ter (step 7).
due to the β-effect of the silicon atom.[55] However, only
alkynic and allenic hydrocarbons are addressed in detail
within this paper. Consequently, only steric factors have to
be considered. Thus, according to Magnus mechanism,
complexation of the less substituted double bond of the all-
enic hydrocarbon 3 to the intermediate alkyne–pentacar-
bonyldicobalt complex I would preferentially occur anti to
the R group (RϾϾRЈ) and also anti to the allenic substitu-
ent R1 through the less hindered half-space defined by the
allenic unit (Scheme 8). This coordination should result in
the bending of the allenic ligand and would lead to the π
complex A-anti.[56] Then, the insertion of the allenic unit
into the adjacent RЈC–Co bond would give the σ-allyl co-
baltacycle B-anti (path a) from which the cyclopentenone
(E)-4 would be generated after further elementary steps of
the PKR (CO insertion into the allylic C–Co bond giving
the acylcobalt complex C, followed by a reductive elimi-
nation of cobalt to give complex D and decomplexation
from Co2Ln). Likewise, the π complex A-syn would give the
minor cyclopentenone (Z)-4 (path b). The high E-stereose-
lectivity (E/ZՆ95:5 when RЈ ϶ H and E/Z ≈ 75:25 when
RЈ = H) would result from the large steric interaction be-
tween the RЈ and R1 groups within this last A-syn π com-
plex. Formation of the minor regioisomeric cyclopentenone
5 could be explained from another, less favored (=CR1R2/
Co–CϵO steric interactions) π complex E obtained by the
coordination of the allenic unit through its more substituted
double bond (path c). Insertion of the allene would lead to
complex F and, finally, to cyclopentenone 5. The isomer 5-
alkylidenecyclopentenone (6) might emerge from the fourth
π complex G (a rotamer of the A-anti π complex) through
the insertion of the allene into the RЈC–Co bond leading
Scheme 7. PKR Magnus mechanism.
Evidence for the involvement of putative intermediates I to the σ-vinyl cobalt complex H, followed by the three final
and II has recently been obtained, and several refinements steps (path d).
to this primary Magnus pathway, particularly about the ole-
However, as qualitatively shown by using molecular
fin coordination and insertion steps (steps 3 and 4) have models, the steric interactions of the RЈ (alkyl or H) group
been made. Indeed, photochemically generated type-I inter- of the alkyne unit with the R1 or R2 (alkyl or H) groups of
mediates have been identified by IR spectroscopy,[51] and the allenic hydrocarbon 3 should greatly influence the effec-
intramolecularly chelated intermediates I have been charac- tive formation of these intermediate π complexes A, E and
terized.[19a,52] A stable type-II alkene–pentacarbonyldico- G. Particularly, it seems difficult to understand the forma-
balt cluster was also recently isolated and fully charac- tion, even in small amounts, of cyclopentenones (Z)-4cb (R
terized.[53] For the PKR of norbornene derivatives, the co- = RЈ = Et) and (Z)-4db (R = RЈ = Me) from the A-syn π
ordination of the double bond to cobalt was recently dis- complex generated from complexes 2c and 2d and allene 3b
Eur. J. Org. Chem. 2010, 3312–3336
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F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
Scheme 8. Mechanistic pathways of the PKR of allenic hydrocarbons.
(R1 = nC6H13) because of the large repulsion of the RЈ (Et by Laschat.[26] Such a coordination would give rise to a set
or Me) and R1 (nC6H13) groups (Table 3, entries 6 and 7). of π complexes I–K within dynamic equilibrium for which
On the other hand, the real reasons for the formation of the allenyl ligands should be nearly parallel to the coordi-
the 5-alkylidenecyclopentenones (E)-6ab, (E)-6ac and (E)- nated alkyne triple bond CR–CRЈ.[57] Among them, π com-
6af (see Tables 7 and 8), which are obtained only in the plexes I-anti and I-syn can also explain the formation of
reactions with the acetylene–dicobalt complex 2a, are not cyclopentenones (E)-4 and (Z)-4, respectively (paths e and
totally clear within the Magnus mechanism. Indeed, under- f). As described for π complex E, the intermediate π com-
standing the difference in behavior between the dicobalt plex J may also explain the formation of the regioisomeric
complexes of mono- or disubstituted alkynes 2b–k (R = cyclopentenone 5 (path g). However, for steric reasons, this
alkyl, RЈ = alkyl or H) and complex 2a (R = RЈ = H) with pseudo-axial coordination does not seem as favored when
allenes 3b–h should involve some steric interaction between R is a bulky group such as tert-butyl. Then, the formation
the alkyne group R (or H) and the allenic hydrocarbon 3 of cyclopentenones (E)-4kb and 5kb (Table 5, entry 3) and
and its substituents R1 or R2. This is not the case if the of cyclopentenones 4gb (E and Z) and 5gb (Table 6, entries
initial coordination of the allenic unit takes place anti to 6 and 7) should stem from the intermediate π complexes A
the R group, and should rule out π complex G (and the and E. To rationalize the possible formation of 5-alkylid-
associated path d) as a plausible intermediate π complex enecyclopentenones 6, we looked at the π complex K, which
leading to cyclopentenone (E)-6. The steric interaction be- is a rotamer of the I-anti π complex and features an oppo-
tween the allenic group R2 and the pseudo-equatorial CO site spatial position of the C=CR1R2 group with respect to
ligand might inhibit the formation of this π complex G.
the alkyne CR carbon. This π complex K seems to be the
We envisioned that the coordination of allenes 3 to the only one that presents: (1) a suitable coordination of the
alkyne–pentacarbonyldicobalt complex I may also occur on allenic double bond for the allene insertion (path h), and (2)
a pseudo-axial position (with respect to the Co–Co bond) steric interactions between the R and R2(H) groups, which
of one of the cobalt atoms, as has already been suggested should explain the different reactivities of the dicobalt com-
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Pauson–Khand Reaction of Allenic Hydrocarbons
plexes 2a (R = H) and 2b–f (R ϶ H) as pointed out
above.[7b] Indeed, when R is an alkyl group, these steric in-
teractions disfavor coordination of the allenic unit and the
subsequent production of cyclopentenone 6 (R ϶ H). Actu-
ally, in the PKRs with acetylene 1a (R = RЈ = H), the π
complex K is identical to the I-anti π complex. In this case,
path e is then favored over path h because the formation of
the first C–C bond (step 4 of the PKR; Scheme 7) occurs
preferentially between the alkyne (H)C carbon and the less
bulky internal sp-carbon of the allenic unit (path e) rather
than between this carbon and the allenic CH2 terminus
(path h) (Tables 7 and 8). Furthermore, the latter pathway
h explains the E-configuration of the exo-cyclic double
bond of cyclopentenone (E)-6, because the alkyne R (= H)
and R1 groups should adopt anti positions during the allene
coordination in order to minimize the steric interactions be-
tween these two groups.
Modeling Study
To support the assumption that π complexes I–K are
plausible alternative reaction intermediates, we investigated
the stability of the most relevant species with respect to the
more classical π complexes A–G through DFT calculations.
Thus, we focused our attention on the two formal cycload-
ditions of methylallene (mimic of a monosubstituted allene
3) with propyne (1-alkyne 1) and with acetylene (1a), as
model cycloaddition reactions that are under the steric in-
fluence of the substituent R of 1-alkyne 1. For each of these
reactions we calculated the optimized geometries of the π
complexes A(MeH)-anti, I(MeH)-anti and K(MeH)-anti,
and of A(HH)-anti, G(HH)-anti, and K(HH)-anti, respec-
tively, which could be involved in the different pathways a–
h.
Figure 4. Optimized geometries of the methylallene-coordinated
pentacarbonyldicobalt complexes A–K(RH) at the BPE level. The
relative energies given in brackets (kcalmol–1) for both series of π
complexes (R = CH3 or H) are relative to the more stable com-
plexes A(MeH)-anti and A(HH)-anti, respectively.
DFT calculations were performed with the ADF 08 pro-
gram developed by Baerends and co-workers.[58] The PBE
gradient-corrected exchange-correlation functional,[59] and
the TZP (Triple Zeta plus Polarisation) basis were retained both series (R = Me or H). The different calculated in-
for all the calculations. The frozen core approximation for teratomic bonds of the CRCHCo2 core of these complexes
the inner shells was retained (small core). Relativistic cor- are very close to those calculated for the parent propyne
rections were taken into account with the use of the relativ- and acetylene–dicobalt complexes 2 and 2a (Table 9, entries
istic scalar zero-order regular approximation (ZORA) 5–8).[27c,27f] The interatomic bonds or distances and the
method.[60] All the structures were characterized by vi- angles of the methylallene ligand are given in entries 9–16.
brational analysis in the harmonic approximation. Further- For all complexes, the coordinated methylallene was planar
more, to allow comparison, post-SCF energy calculations and the allenic unit was bent (entry 13: angle C1–C2=C3 =
were performed at the optimized geometries (using the ME- 150–153°). Particularly, the values (67–104°) of the dihedral
TAGGA keyword), providing B3LYP and other GGA ener- angles CH–Co1–C2–C3 for the I(RH)-anti and K(RH)-anti
gies (Figure 4, Table 9). The rather small deviation of the π complexes show that the C1–C2 bond of the coordinated
relative energies with respect to popular excange-correlation allene is nearly parallel to the alkyne bond CR–CH in these
functionals (less than 0.5 kcalmol–1) underlines the reliabil- complexes, as anticipated qualitatively (entry 16), whereas
ity of the calculations within a chemical context.
it is nearly parallel to the CH–Co1 bond for the more classi-
We found localized minima for all six π complexes, and cally postulated A(RH)-anti complexes (dihedral angle CH–
their optimized structures are shown in Figure 4. Their rela- Co1–C2–C3 was 33.5° for R = CH3, and 34.5° for R = H).
tive energies and most important structural features are Consequently, the I(RH)-anti and K(RH)-anti π complexes
given in Table 9. The axially allene-coordinated complexes should also be considered as plausible reaction intermedi-
I(RH)-anti and K(RH)-anti are energetically very close to ates in the Pauson–Khand cycloadditions of allenic com-
the A(RH)-anti π complexes, which were the most stable in pounds.
Eur. J. Org. Chem. 2010, 3312–3336
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F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
Table 9. Relative energies and structural features of the A–K(RH)-anti π complexes.
FULL PAPER
Entry
A(MeH)-anti
I(MeH)-anti
K(MeH)-anti
A(HH)-anti
K(HH)-anti[i]
G(HH)-anti
1
2
3
4
5
6
7
8
∆E(PBE)[a,b]
∆E(PBE0)[a,c]
∆E(B3LYP)[a,d]
∆E(M06)[a,e]
0.0
0.0
0.0
0.0
2.516
1.343
1.984
1.958
2.121
2.054
1.377
1.325
152.4
–
+1.27
+1.40
+1.44
+1.55
2.484
1.339
1.990
1.981
2.078
2.024
1.388
1.326
150.9
–
+1.73
+1.61
+2.19
+1.91
2.479
1.341
2.012
1.957
2.083
2.025
1.387
1.327
150.4
3.089
–
0.0
0.0
0.0
0.0
2.519
1.340
1.966
1.963
2.054
2.118
1.377
1.325
152.5
–
+0.52
+0.28
+0.66
+1.24
2.487
1.338
1.982
1.966
2.083
2.027
1.387
1.326
151.1
3.129
–
+0.97
+1.11
+0.95
+0.96
2.516
1.341
1.966
1.970
2.123
2.080
1.374
1.325
152.8
2.953
–
[f]
Co1–Co2
CR–CH
Co1–CR
Co1–CH
Co1–C1
Co1–C2
C1–C2
9
10
11
12
13
14
15
16
C2=C3
C1–C2=C3
[g]
[h]
CH···C1[h]
CH···C2
2.869
33.5
2.650
67.2
2.863
34.5
[g]
CH–Co1–C2–C3
104.7
97.0
134.3
[a] DFT relative energies are in kcalmol–1. [b] PBE energy: ref.[59] [c] PBE0 energy: ref.[61] [d] B3LYP energy: ref.[62] [e] M06 energy: ref.[63]
[f] Bond and distances are in Å. [g] Angles and dihedral angles are in degrees. [h] Interatomic distances between the future bonded atoms
CH and C1 or C2. [i] For R = H, complex K(HH)-anti is identical to complex I(HH)-anti.
Comparing the relative energies of the different π com- cause both pseudo-equatorial and pseudo-axial coordina-
plexes of both series (R = Me or H) supports our rational- tion of allene 3 to the intermediate pentacarbonyldicobalt
ization of the observed selectivities in the PKRs of allenic complex I appear to be plausible.
hydrocarbons. The small relative energy (+0.52 kcalmol–1)
of complex K(HH)-anti compared to complex A(HH)-anti
allows an understanding of how it may also lead to cyclo-
pentenones (E)-4, as the A(HH)-anti π complex, and to cy-
clopentenone (E)-6 (R = RЈ = H) (paths e and h, respec-
tively), whereas the higher energy of the G(HH)-anti π com-
plex (+0.97) seems to exclude this as a plausible intermedi-
ate in the formation of cyclopentenone (E)-6. The energy
difference between complex I(MeH)-anti and A(MeH)-anti
is larger, due to the presence of the alkyne methyl group,
which makes a pseudo-axial coordination of an allenic unit
less likely. However, it does not seem large enough to ex-
clude I(MeH)-anti as an intermediate (path e). Within this
series of (MeH)-intermediates, complex K(MeH)-anti has a
higher energy (+1.73 kcalmol–1), which may be relevant to
the fact that the regioisomeric cyclopentenone 6 is never
formed in the PKRs of substituted alkynes.
Conclusions
In summary, this work demonstrates that the PKR of
allenic hydrocarbons 3 gives 4-alkylidenecyclopentenones 4
with high regio- and stereoselectivities (E/ZՆ70:30), with
the formation of minor amounts of the regioisomeric cyclo-
pentenones 5 and 6.[64] By studying the relationship be-
tween the selectivity changes to these isomeric cyclopent-
enones 4–6 and the substitution patterns of both the acetyl-
enic and the allenic partners, competitive mechanistic path-
ways could be established from several allene–dicobalt π
complexes A–K, the involvement of which was supported
by DFT calculations on the most relevant species of these
intermediate π complexes. Thus, as far as we are aware, our
experimental results provides evidence for the first time that
the Pauson–Khand reaction may involve both a pseudo-
equatorial and a pseudo-axial coordination of a double
bond to one of the cobalt atoms, leading to two isomeric
cyclopentenones. In particular, the formation of 5-alkylid-
enecyclopentenones 6, which are only obtained from the
acetylene–dicobalt complex 2a, might be rationalized by an
initial pseudo-axial coordination of the allenic unit to co-
balt. This methodology constitutes a general approach to
the synthesis of 4-alkylidenecyclopentenones 4, which has
been fruitfully used for the preparation of functionalized 4-
alkylidenecyclopentenones.[65] Meanwhile, studies on their
reactivity and synthetic applications are being developed in
our group.[66]
To sum up, the cyclopentenones (E)-4 can arise from
both A-anti and I-anti π complexes, and the minor cycload-
ducts (Z)-4 should form preferentially from the I-syn π
complex, and exclusively from the latter when RЈ is an alkyl
group. In contrast, when R is a large tert-butyl group and
RЈ is hydrogen, the A-syn π complex might be involved be-
cause the tert-butyl group disfavors pseudo-axial coordina-
tion of the allenic unit. The regioisomeric cyclopentenones
5 should come from both π complexes E and J, and only
from the E π complex when R is tert-butyl. Finally, the 5-
alkylidenecyclopentenones 6 (R and RЈ = H) may only be
produced from π complex K (identical to I-anti when R =
RЈ = H).
Thus, according to the steric hindrance of the R, RЈ, R1,
and R2 groups of both partners 1 and 3, all pathways a–h,
except path b (when RЈ is an alkyl group), path d and paths
e–g [when R is a bulky group (tBu)], might be involved as
Experimental Section
General: All reactions were carried out under nitrogen in oven-
competitive pathways leading to cyclopentenones 4–6, be- dried glassware using standard syringe, cannula and septa tech-
3324 Eur. J. Org. Chem. 2010, 3312–3336
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Pauson–Khand Reaction of Allenic Hydrocarbons
niques. Tetrahydrofuran was distilled from deep-purple sodium-
benzophenone dianion and stored under nitrogen. Dichlorometh-
ane was distilled from calcium hydride and stored under nitrogen.
Thin-layer chromatography (TLC) was performed using precoated
Kieselgel 60 F254 plates (Merck). Detection was achieved by UV
irradiation (254 nm) followed by charring with 4% p-anisaldehyde,
5% acetic acid and 5% sulfuric acid in 86% ethanol. Flash
chromatography was performed with silica gel 60 (40–63 µm,
Merck) and refers to the procedure of W. C. Still.[67] UV spectra
were recorded with a UV-160A spectrophotometer (Shimadzu).
Absorption bands were measured in ethanol; positions of maxi-
mum absorption bands (λmax) are reported in nm and intensities of
absorption bands are characterized by absorption coefficients (ε)
reported in dm3 mol–1 cm–1. IR spectra were recorded with a Per-
kin–Elmer 298 spectrophotometer from thin films on NaCl plates
for oils or from KBr disc for solids. 1H and 13C NMR spectra were
recorded at 300 or 200 MHz and 75 or 50 MHz, respectively, with
General Procedures for the Pauson–Khand Cycloadditions
Procedure A: To a stirred solution of the alkyne–hexacarbonyldico-
balt complex 2 (1 mmol) in CH2Cl2 (8 mL) at –10 °C, was added a
CH2Cl2 solution (2 mL) of the allenic compound 3 (1.5 mmol). So-
lid NMO (6 mmol) was added in fractions over 5 min and the mix-
ture was warmed to r.t. and stirred overnight (ca. 15 h), during
which a purple precipitate was formed. The mixture was filtered
through a small amount of silica gel (diethyl ether as eluent). The
organic layer was concentrated to dryness under reduced pressure
and the black crude residue obtained was purified by flash
chromatography eluting with PE/Et2O mixtures to afford the alkyl-
idenecyclopentenones 4–6.
Procedure B: To a stirred solution of the alkyne–hexacarbonyldico-
balt complex 2 (1 mmol) in CH2Cl2/THF (1:1, 10 mL) at –78 °C,
was added a CH2Cl2 solution (1 mL) of the allenic hydrocarbon 3
(1.5 mmol). Solid NMO (6 mmol) was then added over 5 min. Af-
ter 15 min at this temperature, the mixture was warmed to r.t. by
removing the cold bath (1 h) and stirring was continued until the
starting complex disappeared (1–3 h). The suspension was filtered
through a small plug of silica gel (washing of the precipitate with
diethyl ether) and concentrated under vacuum. The crude mixture
was diluted with diethyl ether (5–10 mL) and stirred overnight in
order to facilitate the precipitation of cobalt clusters. After fil-
tration and evaporation of ether, the crude product was purified by
flash chromatography (PE/Et2O mixtures as eluent) to afford the
alkylidenecyclopentenones 4–6.
1
a Bruker DRX 300 or an AC 200 instrument. H NMR chemical
shifts were obtained in CDCl3 and are reported in ppm relative to
the solvent shift of residual chloroform at δ = 7.26 ppm. Multi-
plicities are described as: s (singlet), d (doublet), dd, ddd, etc.
(doublet of doublets, doublet of doublets of doublets, etc.), t (trip-
let), q (quartet), m (multiplet), and further qualified as br (broad),
app (apparent); coupling constants (J) are reported in Hz. 13C
NMR chemical shifts were obtained in CDCl3 and are reported in
ppm relative to CHCl3 at δ = 77.16 ppm. All the carbons were
assigned with the aid of Dept 135 experiments. Low and high-reso-
lution mass spectra were obtained with a Thermoquest Finnigan
MAT 95 XL spectrometer in the Electron Impact (EI, ionization
potential of 70 eV) mode or the Chemical Ionization (CI, isobutane
as the reagent gas) mode. Low-resolution mass spectra were also
performed with the ElectroSpray Ionization (ESI) mode. GC/MS
was carried out with a Delsi-DI 700 gas chromatograph fitted with
a DB5 capillary column (30 m), coupled to a Nermag R10–10S
quadrupole mass spectrometer (EI mode at an ionization potential
of 70 eV). Microanalyses were carried out by the “Service Central
d’analyse du CNRS”, Solaize, France. PE refers to petroleum ether
(b.p. 40–60 °C).
Procedure C: To a stirred solution of the alkyne–hexacarbonyldico-
balt complex 2 (1 mmol) in CH2Cl2/THF (1:1, 10 mL) at –78 °C,
was added a CH2Cl2 solution (1 mL) of the allenic hydrocarbon 3
(1.5 mmol). Solid NMO (6 mmol) was then added over 5 min. Af-
ter stirring 2 h at –78 °C, the reaction mixture was slowly warmed
to r.t. over 2 h and then stirred at r.t. for 2 h. Workup and flash
chromatography as described in procedure B afforded alkylidenecy-
clopentenones 4–6.
Procedure D: Performed on 20–40 mmol scale: To a stirred solution
of the alkyne–hexacarbonyldicobalt complex 2 (32 mmol) in a mix-
ture of CH2Cl2 (85 mL) and THF (145 mL) at –40 °C, was added
allene 3 (48 mmol, 1.5 equiv.). A CH2Cl2 (60 mL) solution of NMO
(192 mmol, 6 equiv.) was added dropwise over 40 min while the in-
side temperature was kept at –40 °C. After 30 min at this tempera-
ture, the mixture was warmed to r.t. by removing the cold bath
(about 1 h) and stirring was continued until the starting complex
disappeared (2–4 h). The solution was filtered through silica gel
(washing of the precipitate with diethyl ether) and concentrated
under vacuum. This operation was repeated several times if neces-
sary to eliminate most of the cobalt residue. The crude product was
purified by flash chromatography eluting with PE/Et2O mixtures
to give the corresponding alkylidenecyclopentenones 4–6.
Starting Materials: Octacarbonyldicobalt was purchased from
Strem Chemicals, Inc. as a solid, stabilized with 1–5% hexane, and
was used as received and stored under nitrogen at 0 °C. Acetylene
(1a; dissolved) was purchased from Air Liquide, and alkynes 1b–
k were all commercially available. Allene (1,2-propadiene; 3a) was
purchased from Union Carbide. Nona-1,2-diene (3b),[68] phenylal-
lene (3c),[68] trimethylsilylallene (3d),[69] 3-methyl-1,2-butadiene
(3e),[70] vinylidenecyclohexane (3f),[71] trideca-6,7-diene (3g),[72] 2-
methyldeca-2,3-diene (3i),[72] cyclonona-1,2-diene (3h),[73] and tet-
ramethylallene (3i)[72] were prepared as reported in the literature.
General Procedure for the Preparation of the Alkyne–Hexacarbonyl-
dicobalt Complexes 2a–k: To a solution of Co2(CO)8 (1 equiv.) in
CH2Cl2 [2.5 mL per mmol of Co2(CO)8] at 0 °C, was added alkyne
1a–k (1.2 equiv.), and the mixture was stirred at this temperature
for 30 min. In the case of complex 2a, acetylene gas (after conden-
sation of acetone in a cooled trap) was bubbled through the solu-
tion of Co2(CO)8 for 1 h. The mixture was warmed to r.t. and
stirred until all Co2(CO)8 was consumed (ca. 2–3 h). From an ex-
perimental point of view, the reaction was complete when emission
of carbon monoxide stopped. The mixture was filtered through a
short plug of Celite. Washing with dichloromethane and evapora-
tion of solvent under vacuum with a rotary evaporator (without
heating), gave the crude dicobalt complex 2 as a purple viscous
precipitate. Yields ranged from 95 to 100%.
Remarks on Procedures A–D: (1) Compositions (% molar ratio) of
the crude cyclopentenone mixtures 4–5 (and 6 when R = RЈ = H)
were analyzed by GC (DB5 capillary column). The retention times
of 4–6 were as follows: tR (5)ϽϽtR [(Z)-4] Ͻ tR [(E)-4] Ͻ tR (6);
(2) TLC: the retention factors Rf of cyclopentenones 4–6 were in
the decreasing order: Rf (5)ϾϾRf [(E)-4] Ͼ Rf [(Z)-4] Ͼ Rf (6),
except for the cyclopentenones (E)- and (Z)-4 (R = RЈ = H) pro-
duced in the PKRs with acetylene 1a, which showed the same po-
larity. Consequently, the less polar cyclopentenones 5 were always
very easily isolated from the cyclopentenones (E)- and (Z)-4 by
flash chromatography. These last stereoisomers could also be iso-
lated, but sometimes needed a second chromatographic column to
be completely separated. In contrast, the (E)- and (Z)-4 (R = RЈ =
Eur. J. Org. Chem. 2010, 3312–3336
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3325

F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
H) cyclopentenones, which stemmed from the PKRs of acetylene
1a, could not be separated and were obtained as mixtures.
afforded cyclopentenone 4da (1.07 g, 25%) and the cyclopentene-
1,3-dione 7d (60 mg, 1.4%).
(E)-4-Heptylidene-2,3-dipropylcyclopent-2-enone (4bb): (Table 2, en-
try 2) Following procedure B, cycloaddition of (oct-4-yne)hexacar-
bonyldicobalt complex (2b; 198 mg, 0.5 mmol) with nona-1,2-diene
(3b; 93 mg, 0.75 mmol) promoted by NMO (351 mg, 3 mmol) in
CH2Cl2/THF (1:1, 14 mL) gave, after flash chromatography (PE/
Et2O, 90:10), the cyclopentenones (E)-4bb (98 mg, 75%) and 5bb
(8 mg, 6%).
4da: Brown oil; R = 0.28 (PE/Et O, 70:30). IR (thin film): ν =
˜
f
2
3060, 2960, 2910, 1700 (C=O), 1640, 1610, 1430, 1390, 1380, 1320,
1
1290, 1070, 930, 890 cm–1. H NMR (300 MHz, CDCl3): δ = 5.26
[br. s, 1 H, (C-4)=CHcis], 5.08 [br. s, 1 H, (C-4)=CHtrans], 2.91 (s, 2
H, 5-H), 2.03 [s, 3 H, (C-3)CH3], 1.77 [s, 3 H, (C-2)CH3] ppm.
The 1H NMR spectroscopic data were in full agreement with those
reported in the literature.[44] 13C NMR (75 MHz, CDCl3): δ = 205.0
(C-1, C=O), 162.3 (C-3), 144.6 (C-4), 141.0 (C-2), 107.4 [(C-
4)=CH2], 39.4 (C-5), 11.6 [(C-3)CH3], 8.6 [(C-2)CH3] ppm.
(E)-4bb: Yellow oil; Rf = 0.35 (PE/Et2O, 90:10). UV/Vis (EtOH):
λmax (ε, Lmol–1 cm–1) = 289 (13254) nm. IR (neat): ν = 2960, 2920,
˜
2870, 2850, 1700 (C=O), 1600, 1470, 1380, 1270, 1100, 1080 cm–1.
4,5-Dimethyl-4-cyclopentene-1,3-dione (7d): Brown oil; Rf = 0.20
1H NMR (300 MHz, CDCl3): δ = 5.72 [t, 3J = 7.5 Hz, 1 H, (C-
(PE/Et O, 70:30). IR (thin film): ν = 2970, 2920, 2870, 1740, 1700
˜
2
3
cm–1. 1H NMR (300 MHz, CDCl3): δ = 2.84 [s, 2 H, (C-2)CH2],
2.01 (s, 6 H, 2ϫ CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 200.9
(2ϫ C=O, C-1 and C-4), 156.8 (2ϫ C, C-4 and C-5), 41.2 (C-2),
9.7 (2ϫ CH3) ppm. HRMS (CI): calcd. for C7H9O2 [M + H]+
125.06025; found 125.06049.
4)=CH], 2.87 (s, 2 H, 5-H), 2.47 [t, J = 7.6 Hz, 2 H, (C-3)CH2],
3
3
2.22 [t, J = 7.4 Hz, 2 H, (C-2)CH2], 2.18 [q, J ≈ 7.5 Hz, 2 H, (C-
4)=CH-CH2], 1.63–1.40 (m, 6 H, 3ϫ CH2), 1.35–1.20 (m, 6 H, 3ϫ
CH2), 0.99 (t, J = 7.0 Hz, 3 H, CH3), 0.95 (t, 3J = 7.5 Hz, 3 H,
3
CH3), 0.90 (t, J = 7.1 Hz, 3 H, CH3) ppm. 13C NMR (50 MHz,
3
CDCl3): δ = 205.2 (C-1, C=O), 167.2 (C-3), 142.6 (C-2), 136.2 (C-
4), 125.0 [(C-4)=CH], 37.5 (C-5), 31.7, 30.1, 29.3, 29.1 (4ϫ CH2),
28.3 [(C-3)CH2], 25.7 [(C-2)CH2], 22.8, 22.7 and 22.0 (3ϫ
CH2CH3), 14.5, 14.3 and 14.1 (3ϫ CH3) ppm. MS (EI): m/z (%)
= 262 (23) [M]+, 233 (22) [M+ – C2H5], 178 (100), 149 (55), 121
(20), 107 (19), 91 (24), 79 (16), 55 (33), 43 (58), 41 (74), 29 (45), 27
(21). C18H30O (262.44): calcd. C 82.38, H 11.52; found C 82.53, H
11.47.
2,3-Diethyl-4-heptylidenecyclopent-2-enone (4cb): (Table 3, entry 6)
Following procedure D, cycloaddition of (hex-3-yne)hexacarbonyl-
dicobalt complex (2c; 8.75 g, 23.8 mmol) with nona-1,2-diene (3b;
3.73 g, 30.3 mmol) promoted by NMO (16.70 g, 143 mmol) in 1:1
CH2Cl2/THF (220 mL) gave, after flash chromatography (PE/Et2O,
90:10), the cyclopentenones (E)-4cb (2.6 g, 47%), (Z)-4cb (88 mg,
2%), and 5cb (71 mg, 1%).
(E)-4cb: Colorless oil; Rf = 0.39 (PE/Et2O, 70:30). UV/Vis (EtOH):
5bb: Yellow oil; R = 0.48 (PE/Et O, 90:10). IR (neat): ν = 2960,
˜
f
2
λmax (ε, Lmol–1 cm–1): 289 (16815) nm. IR (neat): ν = 2960, 2920,
2920, 2850, 1700 (C=O), 1460, 1380, 885 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 5.31 [d, 4J = 1.8 Hz, 1 H, (C-4)=CHcis],
5.13 [d, 4J = 0.7 Hz, 1 H, (C-4)=CHtrans], 2.78 (t, 3J = 5.5 Hz, 1 H,
˜
2880, 2860, 1690 (C=O), 1600, 1460, 1385, 1275, 1255, 1235, 1100,
1
1065, 1055, 1040, 1005, 940, 925, 720 cm–1. H NMR (300 MHz,
3
3
CDCl3): δ = 5.74 [t, J = 7.5 Hz, 1 H, (C-4)=CH], 2.87 (s, 2 H, 5-
5-H), 2.49 [t, J = 7.7 Hz, 2 H, (C-3)CH2], 2.28–2.19 [m, 2 H, (C-
3
H), 2.51 [q, J = 7.5 Hz, 2 H, (C-3)CH2], 2.27 [q, 3J = 7.5 Hz, 2
3
2)CH2], 1.63–1.20 (m, 14 H, 7ϫ CH2), 0.99 (t, J = 7.4 Hz, 3 H,
3
3
CH3), 0.91 (t, J = 7.4 Hz, 3 H, CH3), 0.88 (t, 3J = 6.6 Hz, 3 H,
H, (C-2)CH2], 2.15 [q, J ≈ 7.4 Hz, 2 H, (C-4)=CHCH2], 1.49–1.23
3
CH3) ppm. 13C NMR (50 MHz, CDCl3): δ = 208.1 (C-1, C=O),
165.6 (C-3), 148.8 (C-2), 143.6 (C-4, C=CH2), 106.5 [(C-4)=CH2],
48.0 (C-5), 31.6, 30.3 and 29.5 (3ϫ CH2), 28.0 [(C-3)CH2], 25.7
and 25.0 (2ϫ CH2), 22.6, 22.5 and 21.8 (3ϫ CH3CH2), 14.4, 14.2
and 14.1 (3ϫ CH3) ppm.
(m, 8 H, 4ϫ CH2), 1.14 [t, J = 7.5 Hz, 3 H, (C-3)CH2CH3], 1.03
[t, 3J = 7.5 Hz, 3 H, (C-2)CH2CH3], 0.88 (t, 3J = 6.7 Hz, 3 H,
CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 204.8 (C-1,
C=O), 168.2 (C-3), 143.4 (C-2), 135.6 (C-4), 124.7 [(C-4)=CH], 37.3
(C-5), 31.7 (CH2), 30.0 [(C-4)=CHCH2], 29.2, 29.0 and 22.5 (3ϫ
CH2), 19.2 [(C-3)CH2], 16.6 [(C-2)CH2], 14.0, 13.8 and 13.3 (3ϫ
CH2CH3) ppm. MS (CI): m/z = 235 [M + H]+. HRMS (CI): calcd.
for C16H27O [M + H]+ 235.2062; found 235.2069.
2,3-Dimethyl-4-methylenecyclopent-2-enone (4da):[44] (Table 3, entry
1) Following procedure B, a solution of (but-2-yne)hexacarbonyld-
icobalt complex (2d; 2 g, 5.88 mmol) in a 1:1 mixture of CH2Cl2
and THF (30 mL) was stirred at –78 °C in an autoclave. At the
same time, propa-1,2-diene (3a; 0.8 mL, 13.6 mmol) was condensed
at –78 °C, then transferred rapidly through a cannula into the auto-
clave. Solid NMO (4.13 g, 35.28 mmol) was added in one portion
and the autoclave closed. The mixture was stirred at –78 °C for 2 h,
then warmed to r.t. and stirred overnight. The mixture was filtered
through a small plug of silica gel (washing the precipitate with di-
ethyl ether) and the filtrate was concentrated under vacuum. Purifi-
cation of the crude residue by flash chromatography eluting with
a PE/Et2O, 80:20 mixture afforded cyclopentenone 4da (423 mg,
59%).
(Z)-4cb: Colorless oil; Rf = 0.33 (PE/Et2O, 70:30). IR (thin film):
ν = 2960, 2920, 2880, 2860, 1690 (C=O), 1600, 1460, 1385, 1275,
˜
1
1255, 1235, 1100, 1065, 1055, 1040, 1005, 940, 925, 720 cm–1. H
NMR (300 MHz, CDCl3): δ = 5.33 [t, 3J = 7.8 Hz, 1 H, (C-4)=CH],
2.93 (s, 2 H, 5-H), 2.64 [q, 3J = 7.6 Hz, 2 H, (C-3)CH2], 2.37 [q, 3J
= 7.4 Hz, 2 H, (C-2)CH2], 2.26 [m, 2 H, (C-4)=CHCH2], 1.49–1.23
3
[m, 8 H, 4ϫ CH2], 1.15 [t, J = 7.6 Hz, 3 H, (C-3)CH2CH3], 1.02
[t, 3J = 7.4 Hz, 3 H, (C-2)CH2CH3], 0.88 (t, 3J = 6.7 Hz, CH3)
ppm. 13C NMR (75 MHz, CDCl3): δ = 205.4 (C-1, C=O), 167.7
(C-3), 143.8 (C-2), 133.8 (C-4), 128.4 [(C-4)=CH], 42.8 (C-5), 32.1,
30.7, 29.5 and 29.1 (4ϫ CH2), 23.0 [(C-3)CH2], 22.3 (CH2), 16.7
[(C-2)CH2], 14.5, 14.1 and 13.9 (3ϫ CH2CH3) ppm.
Reaction on a preparative scale (35 mmol): (Table 3, entry 3) Fol-
lowing procedure B as described above, a solution of complex 2d
(11.89 g, 35 mmol) in a 1:4 CH2Cl2/THF mixture (100 mL) was
stirred at –78 °C in an autoclave closed with a septum. Propa-1,2-
diene (3a; 4.5 mL, 77.6 mmol) and a solution of NMO (25.4 g,
1
5cb: Yellow oil; Rf = 0.30 (PE/Et2O, 90:10). H NMR (300 MHz,
CDCl3): δ = 5.32 [br. s, 1 H, (C-4)=CHcis], 5.13 [br. s, 1 H, (C-
4)=CHtrans], 2.76 [t, 3J = 5.6 Hz, 1 H, (C-5)H], 2.46 [q, 3J = 7.7 Hz,
3
2 H, (C-3)CH2], 2.30 [q, J = 7.6 Hz, 2 H, (C-2)CH2], 1.67 [m, 2
3
210 mmol) in CH2Cl2 (60 mL) were successively added through a H, (C-5)CH2], 1.49–1.23 (m, 8 H, 4ϫ CH2), 1.15 [t, J = 7.7 Hz, 3
3
cannula into the autoclave at –78 °C. The autoclave was then closed
and the mixture was warmed to r.t. and stirred overnight. After
workup as described above, the purification of the crude residue
by two successive flash chromatographic columns (PE/Et2O, 80:20)
H, (C-3)CH2CH3], 1.02 [t, J = 7.6 Hz, 3 H, (C-2)CH2CH3], 0.85
3
(t, J = 6.7 Hz, 3 H, CH2CH3) ppm. 13C NMR (75 MHz, CDCl3):
δ = 208.4 (C-1, C=O), 167.0 (C-3), 148.6 (C-4), 144.8 (C-2), 106.7
[(C-4)=CH2], 48.4 (C-5), 32.0, 30.6, 30.0, 25.3 and 23.0 (5ϫ CH2),
3326
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 3312–3336

Pauson–Khand Reaction of Allenic Hydrocarbons
19.4 [(C-3)CH2], 17.1 [(C-2)CH2], 14.4, 14.2 and 13.6 (3ϫ MS (EI): m/z (%) = 254 (100) [M]+, 239 (24) [M+ – CH3], 225 (64)
CH2CH3) ppm.
[M+ – C2H5], 211 (22) [M+ – C3H7], 135 (35), 91 (50), 77 (15), 41
(18).
4-Heptylidene-2,3-dimethylcyclopent-2-enone (4db): (Table 3, entry
7) Following procedure B, cycloaddition of (but-2-yne)dicobalthe-
xacarbonyl complex (2d; 3.91 g, 11.5 mmol) with nona-1,2-diene
(3b; 2.15 g, 17.25 mmol) promoted by NMO (8.08 g, 69 mmol) in
1:1 CH2Cl2/THF (65 mL) gave, after flash chromatography (PE/
Et2O, 90:10), the cyclopentenones (E)-4db (1.86 g, 78%), (Z)-4db
(77 mg, 3%), and 5db (232 mg, 10%).
(E)-2,3-Dipropyl-4-[(trimethylsilyl)methylene]cyclopent-2-enone (4bd):
(Table 3, entry 12) Following procedure B, cycloaddition of (oct-4-
yne)dicobalthexacarbonyl complex (2b; 770 mg, 1.94 mmol) with
trimethylsilylallene (3d; 327 mg, 2.91 mmol) promoted by NMO
(1.36 g, 11.64 mmol) gave, after flash chromatography (PE/Et2O,
92:8), the cyclopentenone (E)-4bd (290 mg, 61%).
(E)-4bd: Colorless oil; Rf = 0.38 (PE/Et2O, 90:10). UV (EtOH):
λmax (ε, Lmol–1 cm–1) = 204 (34776), 284 (25752) nm. IR (thin film):
(E)-4db: Yellow oil; R = 0.31 (PE/Et O, 90:10). IR (neat): ν = 2960,
˜
f
2
2920, 2860, 1700 (C=O), 1620, 1470, 1400, 1380, 1270, 1080 cm–1.
1H NMR (300 MHz, CDCl3): δ = 5.71 [t, 3J = 7.3 Hz, 1 H, (C-
4)=CH], 2.87 (s, 2 H, 5-H), 2.14 [q, 3J ≈ 7.2 Hz, 2 H, (C-
4)=CHCH2], 2.05 [s, 3 H, (C-3)CH3], 1.79 [s, 3 H, (C-2)CH3], 1.42
ν = 2960, 2920, 2870, 1700 (C=O), 1600, 1460, 1370, 1310, 1250,
˜
1
1190, 1100, 860, 840, 690 cm–1. H NMR (300 MHz, CDCl3): δ =
4
3
5.87 [t, J = 1.4 Hz, 1 H, (C-4)=CH-SiMe3], 2.94 (d, J = 1.4 Hz,
2 H, 5-H), 2.47 [t, 3J = 7.6 Hz, 2 H, (C-3)CH2], 2.24 [t, 3J = 7.4 Hz,
3
(m, 2 H, CH2), 1.15–1.30 (m, 6 H, 3ϫ CH2), 0.88 (t, J = 6.6 Hz,
3
2 H, (C-2)CH2], 1.24–1.60 (m, 4 H, 2ϫ CH3CH2CH2), 1.01 (t, J
= 7.3 Hz, 3 H, CH3), 0.92 (t, J = 7.3 Hz, 3 H, CH3), 0.17 [s, 9 H,
3 H, CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 205.1 (C-1,
C=O), 163.3 (C-3), 138.7 and 137.2 (C-2 and/or C-4), 124.8 [(C-
4)=CH], 37.1 (C-5), 31.7, 29.9, 29.3, 29.0 and 22.6 (5ϫ CH2), 14.0
(CH3), 11.8 [(C-3)CH3], 8.3 [(C-2)CH3] ppm. MS (EI): m/z (%) =
206 (27) [M]+, 135 (17) [M+ – C5H11], 122 (100), 91 (13), 79 (12),
41 (15), 29 (10), 27 (10). HRMS (EI): calcd. for C14H22O [M]+
206.1671; found 206.1670.
3
Si(CH3)3] ppm. 13C NMR (75 MHz, CDCl3): δ = 205.6 (C-1,
C=O), 167.1 (C-3), 150.4 (C-2), 149.3 (C-4), 123.1 [(C-4)=CH], 39.9
(C-5), 27.7 [(C-3)CH2], 25.9 [(C-2)CH2], 22.6 and 21.8 (2ϫ
CH3CH2CH2), 14.5 and 14.3 (2ϫ CH3), –0.4 [3ϫ C, Si(CH3)3]
ppm. MS (EI): m/z (%) = 250 (100) [M]+, 235 (29) [M+ – CH3],
221 (58) [M+ – C2H5], 75 (28), 73 (100), 59 (26), 45 (19). C15H26OSi
(250.46): calcd. C 71.93, H 10.46; found C 71.27, H 10.78. HRMS
(EI): calcd. for C15H26OSi [M]+ 250.1753; found 250.1751.
(Z)-4db: Yellow oil; R = 0.22 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
2960, 2920, 2860, 1700 (C=O), 1620, 1470, 1400, 1380, 1270, 1080
cm–1. 1H NMR (200 MHz, CDCl3): δ = 5.52 [t, 3J = 7.2 Hz, 1
H, (C-4)=CH], 2.95 (s, 2 H, 5-H), 2.43 [q, 3J ≈ 7.2 Hz, 2 H, (C-
4)=CHCH2], 2.27 [s, 3 H, (C-3)CH3], 1.69 [s, 3 H, (C-2)CH3], 1.43–
4-Isopropylidene-2,3-dipropylcyclopent-2-enone (4be): (Table 4, en-
try 1) Following procedure A, cycloaddition of (oct-4-yne)hexa-
carbonyldicobalt complex (2b; 396 mg, 1 mmol) with 1,1-dimeth-
ylallene (3e; 136 mg, 2 mmol) promoted by NMO (702 mg,
6 mmol) gave, after flash chromatography (PE/Et2O, 90:10), the cy-
clopentenones 4be (127 mg, 62%) and 5be (10 mg, 5%).
3
1.15 (m, 8 H, 4ϫ CH2), 0.90 (t, J = 7.0 Hz, 3 H, CH2CH3) ppm.
MS (EI): m/z (%) = 206 (15) [M]+, 122 (100), 107 (25), 91 (15), 79
(11), 77 (10), 27 (11).
5db: Yellow oil; R = 0.40 (PE/Et O, 90:10). IR (neat): ν = 2960,
˜
f
2
4be: Colorless oil; R = 0.23 (PE/Et O, 85:15). IR (thin film): ν =
˜
f
2
2920, 2860, 1700 (C=O), 1620, 1470, 1400, 1380, 1270, 1080 cm–1.
1H NMR (200 MHz, CDCl3): δ = 5.31 [br. s, 1 H, (C-4)=CHcis],
5.12 [br. s, 1 H, (C-4)=CHtrans], 2.81 (t, 3J = 5.5 Hz, 1 H, 5-H),
2.08 [s, 3 H, (C-3)CH3], 1.82 [s, 3 H, (C-2)CH3], 1.82–1.24 (m, 10
2960, 2920, 2870, 1690 (C=O), 1640, 1570, 1460, 1370, 1280, 1230,
1180, 1120, 1090, 1000 cm–1. 1H NMR (200 MHz, CDCl3): δ =
3
3
2.91 (s, 2 H, 5-H), 2.62 [t, J = 8.1 Hz, 2 H, (C-3)CH2], 2.21 [t, J
= 7.7 Hz, 2 H, (C-2)CH2], 2.02 [s, 3 H, C=C(CH3)syn], 1.84 [s, 3 H,
3
H, 5ϫ CH2), 0.87 (t, J = 7.0 Hz, 3 H, CH2CH3) ppm. 13C NMR
3
C=C(CH3)anti], 1.71–1.33 (m, 4 H, 2ϫ CH3CH2CH2), 1.02 (t, J =
7.4 Hz, 3 H, CH3), 0.92 (t, 3J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR
(50 MHz, CDCl3): δ = 205.1 (C-1, C=O), 167.6 (C-3), 144.0 (C-2),
130.2 and 130.0 [C-4 and C=C(CH3)2], 41.4 (C-5), 31.3 [(C-3)CH2],
25.6 [(C-2)CH2], 25.4 [C=C(CH3)cis], 22.8 and 22.4 (2ϫ
CH3CH2CH2), 21.1 [C=C(CH3)trans], 14.5 and 14.4 (2ϫ CH3) ppm.
MS (EI): m/z (%) = 206 (53) [M+], 191 (100) [M+ – CH3], 177 (13)
[M+ – C2H5], 163 (34) [M+ – C3H7], 135 (15), 107 (17), 91 (28), 77
(18), 55 (13), 41 (26).
(50 MHz, CDCl3): δ = 208.0 (C-1, C=O), 161.7 (C-3), 149.6 (C-2),
139.6 (C-4), 106.3 [(C-4)=CH2], 47.8 (C-5), 30.1, 29.7, 29.6, 25.2
and 22.6 (5ϫ CH2), 14.1 (CH3), 11.6 [(C-3)CH3], 8.5 [(C-2)CH3]
ppm. MS (EI): m/z (%) = 206 (20) [M]+, 122 (100), 107 (13), 91
(13), 41 (11).
(E)-4-Benzylidene-2,3-dipropylcyclopent-2-enone (4bc): (Table 3, en-
try 9) Following procedure B, cycloaddition of (oct-4-yne)hexacar-
bonyldicobalt complex (2b; 777 mg, 2 mmol) with phenylallene (3c;
343 mg, 2.95 mmol) promoted by NMO (1.380 g, 11.82 mmol)
gave, after flash chromatography (PE/Et2O, 80:20), cyclopentenone
(E)-4bc (349 mg, 70%).
5be: Colorless oil; Rf = 0.52 (PE/Et2O, 85:15). 1H NMR (200 MHz,
CDCl3): δ = 5.26 [s, 1 H, (C-4)=CHcis], 5.09 [s, 1 H, (C-4)=CHtrans],
2.49 [m, 2 H, (C-3)CH2], 2.15–2.35 [m, 2 H, (C-2)CH2], 1.25–1.70
3
(m, 8 H, 4ϫ CH2), 1.12 [s, 6 H, C(CH3)2], 0.91 (t, J = 7.3 Hz, 3
(E)-4bc: Yellow solid; m.p. 44 °C; Rf = 0.33 (PE/Et2O, 80:20). UV/
Vis (EtOH): λmax (ε, Lmol–1 cm–1) = 294 (18324) nm. IR (thin film):
3
H, CH3), 0.88 (t, J = 7.0 Hz, 3 H, CH3) ppm. GC–MS (EI): m/z
(%) = 206 (53) [M]+, 191 (100) [M+ – CH3], 177 (12) [M+ – C2H5],
163 (34) [M+ – C3H7], 149 (15), 135 (20), 107 (14), 91 (24), 77 (19),
55 (19), 41 (35).
ν = 3060, 3020, 2960, 2930, 2870, 1690 (C=O), 1600, 1490, 1465,
˜
1450, 1380, 1360, 1260, 910, 755, 730, 690 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 7.42–7.22 (m, 5 H, 5ϫ ArH), 6.64 [s, 1 H,
3
2,3-Diethyl-4-isopropylidenecyclopent-2-enone (4ce): (Table 4, entry
2) Following procedure D, cycloaddition of (hex-3-yne)hexacarb-
onyldicobalt complex (2c; 12.28 g, 33.3 mmol) with 1,1-dimethyl-
allene (3e; 3.4 g, 50 mmol) promoted by NMO (24.15 g, 200 mmol)
in CH2Cl2/THF (1:1, 320 mL) gave, after two flash chromato-
graphic columns (PE/Et2O, 80:20), the cyclopentenones 4ce (2.96 g,
50%) and the cyclopentene-1,3-dione 7c (166 mg, 3%).
(C-4)=CH-Ph], 3.24 (s, 2 H, 5-H), 2.61 [t, J = 7.8 Hz, 2 H, (C-3)
CH2], 2.30 [t, 3J = 7.7 Hz, 2 H, (C-2)CH2], 1.64 (sextet, 3J ≈ 7.7 Hz,
3
2 H, CH3CH2CH2), 1.49 (sextet, J ≈ 7.5 Hz, 2 H, CH3CH2CH2),
1.06 (t, 3J = 7.3 Hz, 3 H, CH3), 0.95 (t, 3J = 7.4 Hz, 3 H, CH3)
ppm. 13C NMR (75 MHz, CDCl3): δ = 205.4 (C-1, C=O), 168.6
(C-3), 143.3 (C-2), 137.2 and 137.0 [2ϫ Cquart, C-4 and/or C(Ph)i],
129.4 and 129.1 [2ϫ CH(Ph)m and 2ϫ CH(Ph)o], 128.0 [CH(Ph)
p], 123.3 [(C-4)=CH], 39.8 (C-5), 28.6 [(C-3)CH2], 26.2 [(C-2)CH2],
23.1 and 22.4 (2ϫ CH3CH2CH2), 14.9 and 14.7 (2ϫ CH3) ppm.
4ce: Yellow oil; R = 0.27 (PE/Et O, 70:30). IR (thin film): ν =
˜
f
2
2980, 2940, 2880, 1695 (C=O), 1640, 1590, 1465, 1385, 1290, 1270,
Eur. J. Org. Chem. 2010, 3312–3336
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3327

F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
1190, 1090, 1120, 1055, 1010, 940, 830, 785 cm–1. 1H NMR (PE/Et2O, 80:20), the cyclopentenone 4bh as a yellow oil (172 mg,
3
(200 MHz, CDCl3): δ = 2.88 (s, 2 H, 5-H), 2.66 [t, J = 7.5 Hz, 2
66%): R = 0.28 (PE/Et O, 85:15). IR (thin film): ν = 2970, 2920,
˜
f 2
3
H, (C-3)CH2], 2.23 [q, J = 7.5 Hz, 2 H, (C-2)CH2], 2.03 [s, 3 H,
2850, 1695 (C=O), 1590, 1455, 1375, 930, 720 cm–1. 1H NMR
3
3
3
C=C(CH3)syn], 1.81 [s, 3 H, C=C(CH3)anti], 1.14 (t, J = 7.5 Hz, 3 (200 MHz, CDCl3): δ = 5.74 (dd, J = 11.3, J = 6.4 Hz, 1 H, 4-
H, CH3), 0.99 (t, 3J = 7.5 Hz, 3 H, CH3) ppm. 13C NMR (50 MHz,
H), 2.72 (br. dd, J = 8.7, J = 2.5 Hz, 1 H, 10a-H), 2.51 [t, J =
3
3
3
CDCl3): δ = 205.2 (C-1, C=O), 168.9 (C-3), 145.2 (C-2), 130.5 and 7.8 Hz, 2 H, (C-3)CH2], 2.30–2.50 [m, 1 H + 2 H, 5-H and (C-
3
129.9 [C-4 and C=C(CH3)2], 41.6 (C-5), 22.4 [(C-3)CH2], 16.7 [(C-
3a)=CHCH2], 2.23 [t, J = 7.7 Hz, 2 H, (C-2)CH2], 1.70 (m, 1 H,
2)CH2], 25.1 [C=C(CH3)cis], 21.3 [C=C(CH3)trans], 14.1 and 14.0 5Ј-H), 1.20–1.60 (m, 12 H, 6ϫ CH2), 1.00 (t, 3J = 7.4 Hz, 3 H,
(2ϫ CH3) ppm. HRMS (CI): calcd. for C12H19O [M + H]+ CH3), 0.91 (t, J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR (50 MHz,
3
179.14359; found 179.14362.
CDCl3): δ = 208.3 (C-1, C=O), 166.9 (C-3), 142.8 (C-2), 140.3 (C-
3a), 124.3 [C-4, (C-3a)=CH], 49.3 (C-10a), 29.5, 29.3, 29.2, 28.1,
27.8, 26.7, 26.5, 22.6, 22.1 and 21.8 (10ϫ CH2), 14.3 and 14.1 (2ϫ
CH3) ppm. MS (EI): m/z (%) = 260 (56) [M]+, 245 (20) [M+ – CH3],
231 (29) [M+ – C2H5], 178 (20), 133 (19), 107 (21), 105 (46), 93
(32), 91 (100), 79 (56), 77 (47), 55 (41), 43 (32), 41 (72), 29 (20).
C18H28O (260.44): calcd. C 83.02, H 10.84; found C 82.74, H 10.99.
4,5-Diethyl-4-cyclopentene-1,3-dione (7c): Brown oil; Rf = 0.30 (PE/
Et O, 70:30). IR (thin film): ν = 2970, 2920, 2870, 1740 (C=O),
˜
2
1700, 1630, 1455, 1375, 1350, 12380, 1240, 1120, 1055, 925, 755,
700, 660, 650 cm–1. 1H NMR (300 MHz, CDCl3): δ = 2.83 [s, 2 H,
3
3
(C-2)CH2], 2.47 (q, J = 7.5 Hz, 4 H, 2ϫ CH2CH3), 1.13 (t, J =
7.5 Hz, 6 H, 2ϫ CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 201.1
(2ϫ C=O, C-1 and C-3), 161.1 (2ϫ C, C-4 and C-5), 41.6 (C-2),
17.7 (2ϫ CH2CH3), 13.1 (2ϫ CH3) ppm. HRMS (IC): calcd. for
C9H13O2 [M + H]+ 153.0916; found 153.0921.
5-Hexyl-4-isopropylidene-2,3-dipropylcyclopent-2-enone (4bi) and
(E)-4-Heptylidene-5,5-dimethyl-2,3-dipropylcyclopent-2-enone (5bi):
(Table 4, entry 8) Following procedure B, cycloaddition of the (oct-
4-yne)hexacarbonyldicobalt complex (2b; 748 mg, 1.88 mmol) with
2-methyldeca-2,3-diene (3i; 431 mg, 2.83 mmol) promoted by
NMO (1.32 g, 11.3 mmol) in CH2Cl2 (10 mL) gave, after flash
chromatography (PE/Et2O, 95:5), a mixture of the cyclopentenones
4bi and (E)-5bi (226 mg, 41%, 4bi/5bi 60:40). These could be sepa-
rated by a further chromatographic column.
4-Cyclohexylidene-2,3-dipropylcyclopent-2-enone (4bf): (Table 4, en-
try 4) Following procedure B, cycloaddition of (oct-4-yne)dico-
balthexacarbonyl complex (2b; 396 mg, 1 mmol) with vinylidenecy-
clohexane (3f; 162 mg, 1.5 mmol) promoted by NMO (702 mg,
6 mmol) gave, after flash chromatography (PE/Et2O, 80:20), the cy-
clopentenone 4bf as a yellow oil (185 mg, 75%): Rf = 0.15 (PE/
4bi: Yellow oil; R = 0.18 (PE/Et O, 95:5). IR (thin film): ν = 2960,
˜
f
2
Et O, 85:15). IR (thin film): ν = 2960, 2920, 2870, 1690 (C=O),
˜
2
2920, 2870, 1690 (C=O), 1590, 1470, 1380, 1190, 1090 cm–1. 1H
1640, 1570, 1460, 1370, 1280, 1230, 1180, 1120, 1090, 1000 cm–1.
NMR (300 MHz, CDCl3): δ = 2.80 (dd, 3J = 7.1, 3J = 3.7 Hz, 1
H, 5-H), 2.54 [t, J = 7.7 Hz, 2 H, (C-3)CH2], 2.14 [t, J = 7.4 Hz,
2 H, (C-2)CH2], 1.94 [s, 3 H, (C-4)=C(CH3)cis], 1.80 [s, 3 H, (C-
4)=C(CH3)trans], 1.54–1.13 (m, 14 H, 7ϫ CH2), 0.88 (t, 3J = 7.4 Hz,
3 H, CH3), 0.84 (t, J = 7.5 Hz, 3 H, CH3), 0.81 (t, J = 7.5 Hz, 3
H, CH3) ppm. 13C NMR (50 MHz, CDCl3): δ = 208.6 (C-1, C=O),
167.1 (C-3), 142.4 (C-2), 134.8 (C-4), 128.8 [(C-4)=C(CH3)2], 49.5
(C-5), 31.5, 31.4, 31.2, 29.4 and 25.2 (5ϫ CH2), 24.8 [C=C-
(CH3)cis], 24.3 (CH2), 22.5, 22.4 and 22.0 (3ϫ CH3CH2), 21.1
[C=C(CH3)trans], 14.2, 14.1 and 13.9 (3ϫ CH3) ppm.
1H NMR (200 MHz, CDCl3): δ = 2.92 (s, 2 H, 5-H), 2.61 [t, J =
3
3
3
7.7 Hz, 2 H, (C-3)CH2], 2.48 [m, 2 H, (C-4)=C(CH2)cis], 2.26–2.18
[m, 4 H, (C-4)=C(CH2)trans and (C-2)CH2], 1.62 (m, 6 H, 3ϫ CH2),
1.54 (sextet, 3J = 7.3 Hz, 2 H, CH3CH2CH2), 1.46 (sextet, 3J =
7.3 Hz, 2 H, CH3CH2CH2), 1.00 [t, 3J = 7.3 Hz, 3 H, (C-3)
CH2CH3], 0.92 [t, 3J = 7.3 Hz, 3 H, (C-2)CH2CH3] ppm. 13C NMR
(50 MHz, CDCl3): δ = 204.9 (C-1, C=O), 167.3 (C-3), 144.8 (C-2),
139.1 [(C-4)=C(CH2)5], 126.4 [C-4, C=C(CH2)5], 40.7 (C-5), 34.9,
31.7, 31.0, 28.5, 28.1, 26.5 and 25.4 (7ϫ CH2), 22.4 and 22.2 (2ϫ
CH3CH2CH2), 14.3 (2ϫ CH3) ppm.
3
3
(E)-5bi: Yellow oil; R = 0.32 (PE/Et O, 95:5). IR (thin film): ν =
˜
f
2
(E)-4-Hexylidene-5-pentyl-2,3-dipropylcyclopent-2-enone
(4bg):
2960, 2920, 2870, 1690 (C=O), 1590, 1470, 1380, 1290, 1190 cm–1.
(Table 4, entry 6) Following procedure B, cycloaddition of (oct-
4-yne)hexacarbonyldicobalt complex (2b; 88 mg, 0.22 mmol) with
trideca-6,7-diene (3g; 60 mg, 0.32 mmol) promoted by NMO
(154 mg, 1.32 mmol) in CH2Cl2/THF (1:1, 6 mL) gave, after flash
chromatography (PE/Et2O, 95:5), the cyclopentenone (E)-4bg as a
1H NMR (300 MHz, CDCl3): δ = 5.55 [t, 3J = 7.6 Hz, 1 H, (C-
3
3
4)=CH], 2.38 [t, J = 7.6 Hz, 2 H, (C-3)CH2], 2.25 [t, J = 7.5 Hz,
2 H, (C-2)CH2], 2.16 [q, 3J ≈ 7.6 Hz, 2 H, (C-4)=CHCH2], 1.54–
1.13 (m, 12 H, 6ϫ CH2), 1.11 [s, 6 H, 2ϫ (CH3)gem], 0.90 (t, J =
3
7.2 Hz, 3 H, CH2CH3), 0.82 (t, 3J = 7.2 Hz, 6 H, 2ϫ CH3CH2)
ppm. 13C NMR (50 MHz, CDCl3): δ = 211.2 (C-1, C=O), 165.4
(C-3), 145.6 (C-2), 137.7 (C-4), 125.4 [(C-4)=CH], 44.7 (C-5), 31.6,
29.7, 29.0 and 28.5 (4ϫ CH2), 27.7 [(C-3)CH2], 25.5 [(C-2)CH2],
22.7 [2ϫ (CH3)gem], 22.6, 22.4 and 21.7 (3ϫ CH3CH2), 14.2, 14.0
and 13.8 (3ϫ CH3) ppm.
yellow oil (57 mg, 81%): R = 0.43 (PE/Et O, 95:5). IR (neat): ν =
˜
f
2
2960, 2920, 2870, 1700 (C=O), 1610, 1470, 1380, 1260, 730 cm–1.
1H NMR (300 MHz, CDCl3): δ = 5.67 [t, 3J = 7.5 Hz, 1 H, (C-
3
3
4)=CH], 2.87 (app t, J ≈ 5.1 Hz, 1 H, 5-H), 2.45 [t, J = 7.6 Hz, 2
H, (C-3)CH2], 2.21 [t, 3J = 7.6 Hz, 2 H, (C-2)CH2], 2.15 [q, 3J
≈ 7.5 Hz, 2 H, (C-4)=CHCH2], 1.74–1.17 (m, 18 H, 9ϫ CH2), 0.97
3
3
(t, J = 7.3 Hz, 3 H, CH3), 0.90 (t, J = 7.3 Hz, 6 H, 2ϫ CH3 of
pentyl groups), 0.81 (t, 3J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR
(50 MHz, CDCl3): δ = 208.2 (C-1, C=O), 166.9 (C-3), 141.3 (C-2),
140.1 (C-4), 124.6 [(C-4)=CH], 46.3 (C-5), 31.8, 31.5, 30.2, 29.6
and 29.1 (5ϫ CH2), 27.8 [(C-3)CH2], 25.4 (CH2), 23.7 [(C-2)CH2],
22.4, 22.3, 22.2 and 21.7 (4ϫ CH2CH3), 14.2, 14.1, 13.8 and 13.8
(4ϫ CH3) ppm. MS (EI): m/z (%) = 318 (9) [M]+, 248 (68), 247
(38), 192 (100), 91 (13), 43 (33), 41 (35), 29 (19).
(E)-4-Heptylidene-3-methyl-2-propylcyclopent-2-enone
(4ib):
(Table 5, entry 1) Following the procedure B, cycloaddition of the
(hex-2-yne)hexacarbonyldicobalt complex (2i; 392 mg, 1.05 mmol)
with nona-1,2-diene (3b; 195 mg, 1.57 mmol) promoted by NMO
(738 mg, 6.30 mmol) in CH2Cl2/THF (1:1, 8 mL) gave, after flash
chromatography (PE/Et2O, 90:10), the cyclopentenones (E)-4ib
(141 mg, 57%), (E)-4Јib (35 mg, 14%) and 5ib (30 mg, 12%).
(E)-4ib: Yellow oil; R = 0.26 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
2,3-Dipropyl-6,7,8,9,10,10a-hexahydro-1(5H)-cyclopentacyclononen-
one (4bh): (Table 4, entry 7) Following procedure A, cycloaddition
of the (oct-4-yne)hexacarbonyldicobalt complex (2b; 396 mg,
1 mmol) with cyclonona-1,2-diene (3h; 183 mg, 1.5 mmol) pro-
moted by NMO (702 mg, 6 mmol) gave, after flash chromatography
2960, 2920, 2860, 1700 (C=O), 1610, 1470, 1390, 1090, 920, 730
1
3
cm–1. H NMR (300 MHz, CDCl3): δ = 5.69 [t, J = 7.3 Hz, 1 H,
(C-4)=CH], 2.84 (s, 2 H, 5-H), 2.19 [t, 3J = 7.7 Hz, 2 H, (C-2)CH2],
3
2.11 [q, J ≈ 7.3 Hz, 2 H, (C-4)=CHCH2], 2.03 [s, 3 H, (C-3)CH3],
3
1.40 [sextet, J = 7.7 Hz, 2 H, (C-2)CH2CH2CH3], 1.25 (m, 10 H,
3328
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 3312–3336

Pauson–Khand Reaction of Allenic Hydrocarbons
5ϫ CH2), 0.85 (t, 3J = 7.7 Hz, 2ϫ3 H, 2ϫ CH2CH3) ppm. 13C 5jb: Yellow oil; R = 0.45 (PE/Et O, 90:10). IR (thin film): ν = 3030,
˜
f
2
NMR (75 MHz, CDCl3): δ = 204.8 (C-1, C=O), 163.3 (C-3), 142.9 2950, 2920, 2850, 1700 (C=O), 1445, 1390, 1270, 1180, 910, 89,
1
(C-2), 137.2 (C-4), 125.0 [(C-4)=CH], 37.2 (C-5), 31.7, 30.0, 29.2, 740, 700 cm–1. H NMR (300 MHz, CDCl3): δ = 7.46–7.36 (m, 5
and 29.0 (4ϫ CH2), 25.3 [(C-2)CH2], 22.6 and 21.7 (2ϫ CH2CH3),
14.1 and 14.0 (2ϫ CH2CH3), 11.8 [(C-3)CH3] ppm. MS (EI): m/z
H, 5ϫ ArH), 5.50 [d, 4J = 1.5 Hz, 1 H, (C-4)=CHcis], 5.32 [br. s, 1
H, (C-4)=CHtrans], 3.00 (t, J = 5.5 Hz, 1 H, 5-H), 2.25 [s, 3 H, (C-
3
(%) = 234 (24) [M]+, 205 (19) [M+ – C2H5], 150 (100), 121 (18), 91 3)CH3], 1.28 (m, 10 H, 5ϫ CH2), 0.88 (t, 3J = 6.6 Hz, 3 H,
(27), 77 (21), 41 (34), 29 (18). HRMS (CI): calcd. for C16H26O [M CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 205.8 (C-1,
+ H]+ 235.2062; found 235.2058.
C=O), 161.9 (C-3), 149.5 (C-4), 141.8 (C-2), 131.5 [C(Ph)i], 129.4
[2ϫ CH(Ph)o], 128.1 [2ϫ CH(Ph)m], 128.0 [CH(Ph)p], 108.4 [(C-
4)=CH2], 48.3 (C-5), 31.6, 30.4, 29.5 and 25.2 (4ϫ CH2), 22.6
(CH2CH3), 14.0 (CH2CH3), 12.5 [(C-3)CH3] ppm. MS (EI): m/z
(%) = 268 (50) [M]+, 197 (15) [M+ – C5H11], 185 (16), 184 (100),
183 (11) [M+ – C6H13], 153 (10), 141 (11).
(E)-4Јib: Yellow oil; R = 0.18 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
2960, 2920, 2860, 1700 (C=O), 1610, 1470, 1390, 1090, 920, 730
1
3
cm–1. H NMR (300 MHz, CDCl3): δ = 5.49 [t, J = 7.3 Hz, 1 H,
(C-4)=CH], 2.89 (s, 2 H, 5-H), 2.44 [t, 3J = 7.7 Hz, 2 H, (C-3)CH2],
2.11 [q, 3J ≈ 7.3, Hz, 2 H, (C-4)=CHCH2], 1.76 [s, 3 H, (C-2)CH3],
3
1.48 [sextet, J = 7.7 Hz, 2 H, (C-3)CH2CH2CH3], 1.23 (m, 10 H, (E)-2-tert-Butyl-4-heptylidene-3-methylcyclopent-2-enone
(4kb):
5ϫ CH2), 0.87 (t, 3J = 7.7 Hz, 2ϫ3 H, 2ϫ CH2CH3) ppm. 13C
(Table 5, entry 3) Following procedure B, cycloaddition of the (4,4-
NMR (75 MHz, CDCl3): δ = 205.4 (C-1, C=O), 167.5 (C-3), 138.6 dimethylpent-2-yne)hexacarbonyldicobalt complex (2k; 680 mg,
(C-2), 136.2 (C-4), 124.9 [(C-4)=CH], 37.3 (C-5), 31.8, 30.1, 29.4, 1.78 mmol) with nona-1,2-diene (3b; 332 mg, 2.67 mmol) promoted
and 29.1 (4ϫ CH2), 28.3 [(C-3)CH2], 22.7 and 22.2 (2ϫ CH2CH3),
14.4 and 14.2 (2ϫ CH2CH3), 8.5 [(C-2)CH3] ppm. MS (EI): m/z
by NMO (1.251 g, 10.68 mmol) in CH2Cl2/THF (1:1, 10 mL) gave,
after flash chromatography (PE/Et2O, 97:3), the cyclopentenones
(%) = 234 (13) [M]+, 205 (21) [M+ – C2H5], 150 (100), 135 (21), (E)-4kb (244 mg, 55%) and 5kb (29 mg, 6%).
121 (44), 107 (43), 105 (25), 91 (80), 79 (39), 77 (48), 43 (50), 41
(89), 29 (82), 27 (40).
(E)-4kb: Yellow oil; R = 0.50 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
2960, 2920, 2860, 1700 (C=O), 1640, 1470, 1460, 1380, 1280, 1050,
1
3
4
5ib: Yellow oil; R = 0.36 (PE/Et O, 90:10). IR (thin film): ν = 2960,
850 cm–1. H NMR (300 MHz, CDCl3): δ = 5.74 [tt, J = 7.4, J
˜
f
2
2920, 2860, 1700 (C=O), 1640, 1610, 1470, 1380, 890, 730 cm–1. 1H = 1.6 Hz, 1 H, (C-4)=CH], 2.81 (br. s, 2 H, H-5), 2.22 [s, 3 H, (C-
3
NMR (300 MHz, CDCl3): δ = 5.31 [br. s, 1 H, (C-4)=CHcis], 5.12 3)CH3], 2.11 [q, J ≈ 7.4 Hz, 2 H, (C-4)=CHCH2], 1.43–1.27 (m, 8
3
[br. s, 1 H, (C-4)=CHtrans], 2.80 (t, J = 5.5 Hz, 1 H, 5-H), 2.24 [t, H, 4ϫ CH2), 1.32 (s, 9 H, 3ϫ CH3), 0.87 (t, 3J = 6.8 Hz, 3 H,
3J = 7.3 Hz, 2 H, (C-2)CH2], 2.08 [s, 3 H, (C-3)CH3], 1.24 (m, 12 CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 205.0 (C-1,
H, 6ϫ CH2), 0.87 (t, 3J = 7.3 Hz, 2ϫ3 H, 2ϫ CH2CH3) ppm. MS C=O), 160.9 (C-3), 147.9 (C-2), 137.5 (C-4), 124.2 [(C-4)=CH], 38.3
(EI): m/z (%) = 205 (5) [M+ – C2H5], 150 (100), 135 (10), 121 (17),
107 (20), 105 (15), 91 (93), 79 (18), 77 (61), 43 (46), 41 (96), 29
(81), 27 (39).
(C-5), 34.1 (CMe3), 31.8, 30.1, 29.3 and 29.1 (4ϫ CH2), 30.0 [3ϫ
CH3, C(CH3)3], 22.6 (CH2CH3), 14.1 (CH2CH3), 13.5 [(C-3)CH3]
ppm. MS (EI): m/z (%) = 248 (38) [M]+, 233 (32) [M+ – CH3], 165
(15), 164 (100), 149 (32), 55 (22).
(E)-4-Heptylidene-3-methyl-2-phenylcyclopent-2-enone
(4jb):
(Table 5, entry 2) Following procedure B, cycloaddition of the (1-
phenylpropyne)hexacarbonyldicobalt complex (2j; 740 mg, 1.85
mmol) with nona-1,2-diene (3b; 343 mg, 2.77 mmol) promoted by
NMO (1.293 g, 11.04 mmol) in CH2Cl2/THF (1:1, 12 mL) gave, af-
ter flash chromatography (PE/Et2O, 90:10), the cyclopentenones
5kb: Yellow oil; R = 0.57 (PE/Et O, 90:10). IR (thin film): ν =
˜
f 2
2960, 2920, 2860, 1700 (C=O), 1640, 1470, 1460, 1380, 1280, 1050,
1
4
850 cm–1. H NMR (300 MHz, CDCl3): δ = 5.32 [d, J = 1.5 Hz,
4
1 H, (C-4)=CHcis], 5.07 [d, J = 1.1 Hz, 1 H, (C-4)=CHtrans], 2.69
(br. t, 3J = 5.5 Hz, 1 H, 5-H), 2.24 [s, 3 H, (C-3)CH3], 1.32 (s, 9 H,
(E)-4jb (322 mg, 65%), (Z)-4jb (29 mg, 6%) and 5jb (70 mg, 14%). 3ϫ CH3), 1.30–1.15 (m, 10 H, 5ϫ CH2), 0.86 (t, 3J = 6.6 Hz, 3 H,
CH2CH3) ppm. MS (EI): m/z (%) = 248 (39) [M]+, 233 (28) [M+
–
(E)-4jb: Yellow oil; R = 0.33 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
CH3], 164 (100), 149 (19), 55 (25).
3030, 3010, 2960, 2920, 2850, 1700 (C=O), 1590, 1490, 1440, 1390,
1280, 1170, 940, 910, 760, 730, 700 cm–1. 1H NMR (300 MHz,
4-Methylene-2-propylcyclopent-2-enone (4ea): (Table 6, entry 1) Fol-
lowing procedure B as for the preparation of the cyclopentenone
4da, cycloaddition of the (pent-1-yne)hexacarbonyldicobalt com-
3
CDCl3): δ = 7.45–7.33 (m, 5 H, 5ϫ ArH), 5.93 [t, J = 7.4 Hz, 1
H, (C-4)=CH], 3.08 (s, 2 H, 5-H), 2.22 [m, 2 H, (C-4)=CHCH2],
2.21 [s, 3 H, (C-3)CH3], 1.50 (m, 2 H, CH2), 1.20–1.40 (m, 6 H, plex (2e; 669 mg, 1.9 mmol) with propa-1,2-diene (3a; 1 mL,
3ϫ CH2), 0.92 (t, 3J = 7.0 Hz, 3 H, CH2CH3) ppm. 13C NMR 17 mmol) promoted by NMO (1.32 g, 11.32 mmol) in CH2Cl2/THF
(75 MHz, CDCl3): δ = 202.7 (C-1, C=O), 163.6 (C-3), 141.3 (C-2),
136.9 (C-4), 131.7 [C(Ph)i], 129.3 [2ϫ CH(Ph)o], 128.2 [2ϫ CH-
(1:1, 20 mL) gave, after flash chromatography (PE/Et2O, 90:10), the
cyclopentenone 4ea as a yellow oil (150 mg, 58%). Rf = 0.27 (PE/
(Ph)m], 127.6 [CH(Ph)p], 127.2 [(C-4)=CH], 37.7 (C-5), 31.6, 30.1, Et O, 90:10). IR (thin film): ν = 2960, 2920, 2860, 1710 (C=O),
˜
2
29.1 and 29.0 (4ϫ CH2), 22.5 (CH2CH3), 14.0 (CH2CH3), 12.7 [(C-
1640, 1590, 1460, 1380, 1290, 1190, 1100, 940, 890 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 7.41 (br. s, 1 H, 3-H), 5.26 [br. s, 1 H, (C-
4)=CHcis], 5.14 [br. s, 1 H, (C-4)=CHtrans], 2.98 (s, 2 H, 5-H), 2.24
[t, J = 7.4 Hz, 2 H, (C-2)CH2], 1.54 [sextet, J = 7.4 Hz, 2 H, (C-
2)CH2CH2], 0.93 (t, 3J = 7.4 Hz, 3 H, CH3) ppm. 13C NMR
(75 MHz, CDCl3): δ = 206.0 (C-1, C=O), 153.6 (C-3), 149.1 (C-2),
142.9 (C-4), 110.4 [(C-4)=CH2], 39.7 (C-5), 26.7 [(C-2)CH2], 20.8
[(C-2)CH2CH2], 13.8 (CH3) ppm. MS (EI): m/z (%) = 136 (54)
[M]+, 121 (12) [M+ – CH3], 108 (28), 107 (11) [M+ – C2H5], 93 (61)
[M+ – C3H7], 91 (28), 79 (90), 77 (100), 66 (21), 65 (30), 63 (16),
55 (12).
3)CH3] ppm. MS (EI): m/z (%) = 268 (66) [M]+, 197 (19) [M+
C5H11], 184 (100), 183 (14) [M+ – C6H13], 154 (12), 141 (14).
–
3
3
(Z)-4jb: Yellow oil; Rf = 0.22 (PE/Et2O, 90:10). 1H NMR
3
(300 MHz, CDCl3): δ = 7.50–7.30 (m, 5 H, 5ϫ ArH), 5.71 [t, J =
7.3 Hz, 1 H, (C-4)=CH], 3.14 (s, 2 H, 5-H), 2.50 [m, 2 H, (C-
4)=CHCH2], 2.39 [s, 3 H, (C-3)CH3], 1.20–1.60 (m, 8 H, 4ϫ CH2),
0.89 (t, 3J = 7.0 Hz, 3 H, CH2CH3) ppm. 13C NMR (75 MHz,
CDCl3): δ = 203.5 (C-1, C=O), 163.2 (C-3), 143.9 (C-2), 134.8 (C-
4), 132.0 [C(Ph)i], 129.3 [2ϫ CH(Ph)o], 128.8 [2ϫ CH(Ph)m], 128.0
[CH(Ph)p], 127.9 [(C-4)=CH], 42.6 (C-5), 30.7, 29.1, 29.0 and 26.6
(4ϫ CH2), 22.5 (CH2CH3), 14.0 (CH2CH3), 17.9 [(C-3)CH3] ppm. 4-Heptylidene-2-propylcyclopent-2-enone (4eb): (Table 6, entry 3)
MS (EI): m/z (%) = 268 (84) [M]+, 197 (19) [M+ – C5H11], 184
(100), 183 (14) [M+ – C6H13], 154 (12), 153 (16), 141 (16).
Following procedure B, cycloaddition of the (1-pentyne)hexacar-
bonyldicobalt complex (2e; 292 mg, 0.82 mmol) with nona-1,2-
Eur. J. Org. Chem. 2010, 3312–3336
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3329

F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
diene (3b; 153 mg, 1.23 mmol) promoted by NMO (574 mg,
MS (EI): m/z (%) = 254 (64) [M]+, 183 (60), 170 (100), 155 (36),
4.9 mmol) in CH2Cl2/THF (1:1, 10 mL) gave, after flash 153 (33), 141 (32), 129 (20), 128 (32), 115 (34), 77 (28) [Ph+], 43
chromatography (PE/Et2O, 90:10), the cyclopentenones (E)-4eb
(86 mg, 48%), (Z)-4eb (37 mg, 20%) and 5eb (22 mg, 12%).
(20), 41 (34), 29 (31), 27 (24).
(Z)-4fb: Yellow oil; R = 0.33 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
(E)-4eb: Yellow oil; R = 0.32 (PE/Et O, 90:10). IR (thin film): ν =
˜
3080, 3050, 3020, 2950, 2920, 2850, 1700 (C=O), 1600, 1490, 1120,
f
2
930, 760, 690 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.19 (s, 1 H,
2960, 2920, 2870, 1700 (C=O), 1590, 1460, 1380, 1300, 1050, 930,
730 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.37 (s, 1 H, 3-H),
4
3-H), 7.80 (dd, 3Jo = 8.1, Jm = 1.1 Hz, 2 H, 2ϫ Ho), 7.36 (m, 3
4
5.67 [tt, 3J = 7.4, Jtransoid = 1.7 Hz, 1 H, (C-4)=CHCH2], 2.91
3
H, 2ϫ Hm and 1ϫ Hp), 5.72 [t, J = 7.4 Hz, 1 H, (C-4)=CHCH2],
4
(d, Jtransoid = 1.7 Hz, 2 H, 5-H), 2.25 [q, 3J ≈ 7.4 Hz, 2 H, (C-4,
3.17 (s, 2 H, 5-H), 2.37 [q, 3J ≈ 7.4 Hz, 2 H, (C-4)=CHCH2], 1.66–
C=CHCH2)], 2.12 [t, 3J = 7.3 Hz, 2 H, (C-2)CH2], 1.58–1.22 (m,
10 H, 5ϫ CH2), 0.89 (t, 3J = 6.2 Hz, 6 H, 2ϫ CH3) ppm. 13C
NMR (50 MHz, CDCl3): δ = 205.9 (C-1, C=O), 154.3 (C-3), 146.7
(C-2), 136.2 (C-4), 128.6 [(C-4)=CH], 37.9 (C-5), 31.8, 30.1, 29.3
and 29.1 (4ϫ CH2), 26.5 [(C-2)CH2], 22.7 and 21.2 (2ϫ CH3CH2),
14.3 and 14.1 (2ϫ CH3) ppm. MS (EI): m/z (%) = 220 (62) [M]+,
191 (26) [M+ – C3H7], 149 (21), 136 (100), 121 (22), 108 (46), 107
(23), 93 (34), 91 (35), 79 (53), 77 (38), 65 (20). HRMS (EI): calcd.
for C15H26O [M]+ 220.1827; found 220.1822.
1.24 (m, 8 H, 4ϫ CH2), 0.90 (t, J = 6.6 Hz, 3 H, CH3) ppm. 13C
3
NMR (50 MHz, CDCl3): δ = 203.6 (C-1, C=O), 148.9 (C-3), 142.4
(C-2), 135.6 and 133.6 [C-4 and/or C(Ph)i], 130.0 [(C-4)=CHCH2],
128.4 [2ϫ CH(Ph)m and CH(Ph)p], 127.3 [2ϫ CH(Ph)o], 41.9 (C-
5), 31.7, 29.7, 28.9, 28.6 and 22.5 (5ϫ CH2), 14.2 (CH3) ppm. MS
(EI): m/z (%) = 254 (60) [M]+, 183 (70), 170 (100), 155 (36), 153
(54), 141 (40), 129 (38), 128 (29), 115 (41), 77 (28) [Ph]+, 43 (30),
41 (56), 29 (40), 27 (25).
5fb: Yellow oil; R = 0.50 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
(Z)-4eb: Yellow oil; R = 0.26 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
3080, 3050, 3020, 2950, 2920, 2850, 1700 (C=O), 1600, 1490, 1120,
930, 760, 690 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.90 (s, 1 H,
2960, 2920, 2870, 1700 (C=O), 1590, 1460, 1380, 1300, 1050, 930,
730 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.68 (s, 1 H, 3-H),
3
3-H), 7.84 (d, Jortho = 7.4 Hz, 2 H, 2ϫ Ho), 7.42–7.35 (m, 3 H,
4
5.55 [t, 3J = 7.8, Jcisoid ≈ 0.7 Hz, 1 H, (C-4)=CHCH2], 2.97 (d,
2ϫ Hm and 1ϫ Hp), 5.45 [br. s, 1 H, (C-4)=CHcis], 5.30 [br. s, 1
H, (C-4)=CHtrans], 3.02 (t, 3J = 5.4 Hz, 1 H, 5-H), 1.40–1.19 (m,
10 H, 5ϫ CH2), 0.86 (t, 3J = 6.6 Hz, 3 H, CH3) ppm. MS (EI):
m/z (%) = 254 (60) [M]+·, 183 (18), 170 (100), 155 (8), 153 (9), 141
(5), 55 (7).
4Jcisoid ≈ 0.7 Hz, 2 H, 5-H), 2.30 [m, 2 H, (C-4)=CHCH2], 2.12 [t,
3J = 7.3 Hz, 2 H, (C-2)CH2], 1.58–1.22 (m, 10 H, 5ϫ CH2), 0.89
3
(t, J = 6.2 Hz, 6 H, 2ϫ CH3) ppm. 13C NMR (50 MHz, CDCl3):
δ = 206.6 (C-1, C=O), 149.3 (C-3), 147.9 (C-2), 134.3 (C-4), 127.4
[(C-4)=CH], 40.8 (C-5), 31.7, 30.9, 28.4 and 27.6 (4ϫ CH2), 25.1
[(C-2)CH2], 22.7 and 22.5 (2ϫ CH3CH2), 14.1 and 14.0 (2ϫ CH3)
ppm. MS (EI): m/z (%) = 220 (100) [M]+, 191 (28) [M+ – C3H7],
149 (23), 136 (83), 121 (19), 108 (44), 107 (16), 93 (22), 91 (28), 79
(47), 77 (43), 65 (25).
2-tert-Butyl-4-heptylidenecyclopent-2-enone (4gb): (Table 6, entry 7)
Following procedure B, cycloaddition of the (3,3-dimethylbut-1-
yne)hexacarbonyldicobalt complex (2g; 385 mg, 1.05 mmol) with
nona-1,2-diene (3b; 196 mg, 1.57 mmol) promoted by NMO
(738 mg, 6.3 mmol) in CH2Cl2/THF (1:1, 12 mL) gave, after flash
chromatography (PE/Et2O, 95:5), the cyclopentenones (E)-4gb
(111 mg, 45%), (Z)-4gb (48 mg, 19%) and 5gb (14 mg, 6%).
5eb: Yellow oil; R = 0.45 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
2960, 2920, 2870, 1700 (C=O), 1590, 1460, 1380, 1300, 1050, 930,
730 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.34 (s, 1 H, 3-H),
5.20 [br. s, 1 H, (C-4)=CHtrans], 5.08 [br. s, 1 H, (C-4)=CHcis], 2.76
(app t, 3J ≈ 5.3 Hz, 1 H, 5-H), 2.18 [t, 3J = 7.4 Hz, 2 H, (C-2)CH2],
(E)-4gb: Yellow oil; R = 0.40 (PE/Et O, 95:5). IR (thin film): ν =
˜
f
2
2960, 2920, 2850, 1700 (C=O), 1460, 1360, 1320, 980, 930 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 7.33 (s, 1 H, 3-H), 5.65 [t, 3J =
7.4 Hz, 1 H, (C-4)=CHCH2], 2.90 (s, 2 H, 5-H), 2.11 [q, 3J
≈ 7.4 Hz, 2 H, (C-4)=CHCH2], 1.41–1.23 (m, 8 H, 4ϫ CH2), 1.21
3
1.48 [sextet, J = 7.4 Hz, 2 H, CH3CH2CH2(C-2)], 1.19 (m, 10 H,
3
3
5ϫ CH2), 0.87 (t, J = 7.4 Hz, 3 H, CH3), 0.80 (t, J = 6.2 Hz, 3
H, CH3 of hexyl) ppm. 13C NMR (50 MHz, CDCl3): δ = 208.9 (C-
1, C=O), 153.2 (C-3), 148.2 and 147.7 (C-2 and/or C-4), 109.4 [(C-
4)=CH2], 48.5 (C-5), 31.6, 29.8, 29.4, 26.8 and 25.2 (5ϫ CH2), 22.5
and 20.9 (2ϫ CH2CH3), 14.0 and 13.8 (2ϫ CH3) ppm. MS (EI):
m/z (%) = 220 (34) [M]+, 191 (37) [M+ – C3H7], 136 (35), 108 (15),
91 (16), 79 (33), 77 (31), 97 (15), 55 (100).
3
(s, 9 H, 3ϫ CH3), 0.88 (t, J = 7.0 Hz, 3 H, CH3) ppm. 13C NMR
(75 MHz, CDCl3): δ = 204.7 (C-1, C=O), 153.9 (C-3), 153.1 (C-2),
135.4 (C-4), 128.5 [(C-4)=CHCH2], 39.0 (C-5), 31.9 [C(tBu)], 31.7,
30.0, 29.2 and 29.0 (4ϫ CH2), 28.4 [3ϫ CH3(tBu)], 22.6
(CH2CH3), 14.1 (CH2CH3) ppm. MS (EI): m/z (%) = 234 (60)
[M]+, 219 (32) [M+ – CH3], 163 (26), 150 (100), 149 (21), 135 (35),
107 (21), 91 (21), 79 (19), 77 (21), 57 (20) [tBu]+, 55 (52).
4-Heptylidene-2-phenylcyclopent-2-enone (4fb): (Table 6, entry 5)
Following procedure B, cycloaddition of the phenylacetylene-hexa-
carbonyldicobalt complex (2f; 1.094 g, 2.82 mmol) with nona-1,2-
diene (3b; 526 mg, 4.23 mmol) promoted by NMO (1.980 g,
16.91 mmol) in CH2Cl2/THF (1:1, 14 mL) gave, after flash
chromatography (PE/Et2O, 90:10), cyclopentenones (E)-4fb
(306 mg, 43%), (Z)-4fb (136 mg, 19%) and 5fb (50 mg, 7%).
(Z)-4gb: Yellow oil; R = 0.32 (PE/Et O, 95:5). IR (thin film): ν =
˜
f
2
2960, 2920, 2850, 1700 (C=O), 1460, 1360, 1320, 980, 930 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 7.63 (s, 1 H, 3-H), 5.52 [t, 3J =
7.4 Hz, 1 H, (C-4)=CHCH2], 2.94 (s, 2 H, C-5), 2.27 [q, 3J ≈ 7.4 Hz,
2 H, (C-4)=CHCH2], 1.41–1.23 (m, 8 H, 4ϫ CH2), 1.23 (s, 9 H,
3ϫ CH3), 0.88 (t, 3J = 7.0 Hz, 3 H, CH3) ppm. 13C NMR
(75 MHz, CDCl3): δ = 205.4 (C-1, C=O), 155.1 (C-2), 147.2 (C-3),
133.5 (C-4), 127.3 [(C-4)=CHCH2], 42.0 (C-5), 33.6 (CH2), 32.2
[C(tBu)], 29.7, 29.5 and 28.9 (3ϫ CH2), 28.3 [3ϫ CH3(tBu)], 22.6
(CH2CH3), 14.1 (CH2CH3) ppm. MS (EI): m/z (%) = 234 (100)
[M]+, 219 (43) [M+ – CH3], 191 (20), 107 (15), 149 (21), 135 (26),
107 (15), 77 (16), 57 (19) [tBu]+, 55 (46).
(E)-4fb: Yellow oil; R = 0.38 (PE/Et O, 90:10). IR (thin film): ν =
˜
f
2
3080, 3050, 3020, 2950, 2920, 2850, 1700 (C=O), 1600, 1490, 1120,
930, 760, 690 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.87 (s, 1 H,
4
3-H), 7.80 (dd, 3Jo = 8.1, Jm = 1.1 Hz, 2 H, 2ϫ Ho), 7.36 (m, 3
3
H, 2ϫ Hm and 1ϫ Hp), 5.88 [t, J = 7.4 Hz, 1 H, (C-4)=CHCH2],
3.12 (s, 2 H, 5-H), 2.22 [q, 3J ≈ 7.4 Hz, 2 H, (C-4)=CHCH2], 1.66–
3
1.24 (m, 8 H, 4ϫ CH2), 0.90 (t, J = 6.6 Hz, 3 H, CH3) ppm. 13C
NMR (50 MHz, CDCl3): δ = 203.5 (C-1, C=O), 154.5 (C-3), 141.5 5gb: Yellow oil; R = 0.48 (PE/Et O, 95:5). IR (thin film): ν = 2960,
˜
f
2
(C-2), 135.6 and 131.6 [C-4 and C(Ph)i], 131.3 (C=CHCH2), 128.4
2920, 2850, 1700 (C=O), 1460, 1360, 1320, 980, 930 cm–1. 1H NMR
[2ϫ CH(Ph)m and CH(Ph)p], 127.1 [2ϫ CH(Ph)o], 38.9 (C-5), 31.6, (300 MHz, CDCl3): δ = 7.35 (s, 1 H, 3-H), 5.24 [br. s, 1 H, (C-
3
30.3, 29.1 and 29.0 (4ϫ CH2), 22.6 (CH2CH3), 14.1 (CH3) ppm. 4)=CHtrans], 5.11 [br. s, 1 H, (C-4)=CHcis], 2.78 (t, J = 5.5 Hz, 1
3330
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 3312–3336

Pauson–Khand Reaction of Allenic Hydrocarbons
3
H, 5-H), 1.30–1.16 (m, 10 H, 5ϫ CH2), 1.23 (s, 9 H, 3ϫ CH3), (sextet, 3J ≈ 7.3 Hz, CH2CH2CH3), 0.91 (t, J = 7.3 Hz, CH2CH3),
0.86 (t, 3J = 6.6 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): 0.12 [s, 9 H, Si(CH3)3] ppm. 13C NMR (50 MHz, CDCl3): δ = 206.6
δ = 208.1 (C-1, C=O), 155.5 (C-2), 151.4 (C-3), 147.6 (C-4), 109.5 (C-1, C=O), 156.3 (C-3), 150.2 (C-2), 148.1 (C-4), 128.2 [(C-
[(C-4)=CH2], 49.5 (C-5), 32.1 [C(tBu)], 31.7, 29.9 and 29.5 (3ϫ
4)=CH], 40.2 (C-5), 26.7 [(C-2)CH2], 21.0 (CH2CH3), 13.9
CH2), 28.3 [3ϫ CH3(tBu)], 25.0 (CH2), 22.6 (CH2CH3), 14.1 (CH2CH3), –0.50 [3ϫ Si(CH3)3] ppm.
(CH2CH3) ppm. MS (EI): m/z (%) = 234 (71) [M]+, 219 (18) [M+
–
(Z)-4ed: Yellow oil; Rf = 0.28 (PE/Et2O, 92:8). 1H NMR (300 MHz,
CDCl3): δ = 7.52 (s, 1 H, 3-H), 5.70 [s, 1 H, (C-4)=CH-SiMe3],
CH3], 177 (83) [M+ – tBu], 164 (100), 163 (23), 150 (39), 149 (30),
91 (16), 77 (14), 57 (55) [tBu]+, 55 (60).
3
3
2.87 (s, 2 H, 5-H), 2.42 [t, J = 7.3 Hz, (C-2)CH2], 1.50 (sextet, J
3
4-Benzylidene-2-propylcyclopent-2-enone (4ec): (Table 6, entry 8)
Following procedure B, cycloaddition of the (pent-1-yne)hexacar-
bonyldicobalt complex (2e; 347 mg, 0.98 mmol) with phenylallene
(3c; 170 mg, 1.47 mmol) promoted by NMO (689 g, 5.88 mmol) in
CH2Cl2/THF (1:1, 12 mL) gave, after flash chromatography (PE/
Et2O, 85:15), the cyclopentenones (E)-4ec (108 mg, 52%), (Z)-4ec
(35 mg, 17%) and 5ec (30 mg, 14%).
= 7.3 Hz, CH2CH2CH3), 0.91 (t, J = 7.3 Hz, CH2CH3), 0.18 [s, 9
H, Si(CH3)3] ppm.
2-Phenyl-4-[(trimethylsilyl)methylene]cyclopent-2-enone
(4ef):
(Table 6, entry 10) Following procedure B, cycloaddition of the
(phenylacetylene)hexacarbonyldicobalt complex (2f; 388 mg,
1 mmol) with trimethylsilylallene (3d; 169 mg, 1.5 mmol) promoted
by NMO (703 mg, 6 mmol) in CH2Cl2/THF (1:1, 12 mL) gave, af-
ter flash chromatography (PE/Et2O, 90:10), cyclopentenones (E)-
4fd (98 mg, 42%) and (Z)-4fd (11 mg, 4%).
(E)-4ec: Yellow oil; R = 0.28 (PE/Et O, 85:15). IR (thin film): ν =
˜
f
2
3060, 3020, 2960, 2920, 2860, 1700 (C=O), 1610, 1490, 1450, 1380,
1250, 1190, 1100, 930, 850, 760, 740, 690 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 7.53 (s, 1 H, 3-H), 7.42–7.33 (m, 3 H, 2ϫ
(E)-4fd: Yellow oil; R = 0.40 (PE/Et O, 90:10). IR (neat): ν = 3030,
˜
f
2
2860, 1700 (C=O), 1600, 1440, 1260, 1250, 1140, 1120, 910, 840,
3
4
Hm and 1ϫ Hp), 7.27 (dd, Jo = 5.9, Jm = 1.5 Hz, 2 H, 2ϫ Ho),
1
730, 690 cm–1. H NMR (300 MHz, CDCl3): δ = 7.82 (s, 1 H, 3-
3
6.56 [s, 1 H, (C-4)=CHPh], 3.27 (s, 2 H, 5-H), 2.29 [t, J = 7.3 Hz,
H), 7.78 (m, 2 H, 2ϫ Ho), 7.38 (m, 3 H, 2ϫ Hm and 1ϫ Hp), 6.05
[s, 1 H, (C-4)=CH-SiMe3], 3.18 (s, 2 H, 5-H), 0.20 [s, 9 H,
Si(CH3)3] ppm. 13C NMR (50 MHz, CDCl3): δ = 204.5 (C-1,
C=O), 155.6 (C-3), 149.4 (C-2), 131.3 (C-4), 128.9 [C(Ph)i], 128.6
[2ϫ CH(Ph)o], 127.6 [2ϫ CH(Ph)m and CH(Ph)p], 127.5 [(C-
4)=CH], 41.5 (C-5), –0.20 [3ϫ Si(CH3)3] ppm.
2 H, (C-2)CH2], 1.58 [sextet, 3J = 7.3 Hz, 2 H, (C-2)CH2CH2], 0.96
(t, J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ =
3
205.7 (C-1, C=O), 156.7 (C-3), 146.5 (C-2), 136.7 and 136.6 [C-4
and/or C(Ph)i], 128.9 [2ϫ CH(Ph)m], 128.8 [2ϫ CH(Ph)o], 127.8
[CH(Ph)p], 126.5 [(C-4)=CHPh], 39.8 (C-5), 26.9 [(C-2)CH2], 21.2
(CH2CH3), 14.0 (CH3) ppm. MS (EI): m/z (%) = 212 (100) [M]+,
197 (22) [M+ – CH3], 183 (30) [M+ – C2H5], 169 (35) [M+ – C3H7],
155 (42), 153 (30), 141 (24), 115 (45), 91 (20), 77 (20) [Ph]+, 39 (27).
(Z)-4fd: Yellow oil; R = 0.33 (PE/Et O, 90:10). IR (neat): ν = 3080,
˜
f
2
3050, 3020, 2950, 2920, 2850, 1700 (C=O), 1600, 1490, 1120, 930,
1
760, 690 cm–1. H NMR (300 MHz, CDCl3): δ = 8.03 (s, 1 H, 3-
(Z)-4ec: Yellow oil; R = 0.23 (PE/Et O, 85:15). IR (thin film): ν =
˜
f
2
H), 7.80 (m, 2 H, 2ϫ Ho), 7.38 (m, 3 H, 2ϫ Hm and 1ϫ Hp), 5.92
[s, 1 H, (C-4)=CH-SiMe3], 3.32 (s, 2 H, 5-H), 0.27 [s, 9 H, Si-
(CH3)3] ppm.
3060, 3020, 2960, 2920, 2860, 1700 (C=O), 1600, 1490, 1450, 1380,
1
1350, 1120, 750, 730 cm–1. H NMR (300 MHz, CDCl3): δ = 7.92
(s, 1 H, 3-H), 7.55–7.29 (m, 5 H, 5ϫ ArH), 6.57 [s, 1 H, (C-
4)=CHPh], 3.16 (s, 2 H, 5-H), 2.30 [t, 3J = 7.3 Hz, 2 H, (C-2)CH2],
4-Cyclohexylidene-2-pentylcyclopent-2-enone (4hf): (Scheme 3) Fol-
lowing procedure B, cycloaddition of the (hept-1-yne)hexacarbon-
yldicobalt complex (2h; 2.314 g, 6 mmol) with vinylidenecyclohex-
ane (3f; 780 mg, 7.2 mmol) promoted by NMO (4.220 g, 36 mmol)
in CH2Cl2/THF (1:1, 30 mL) gave, after flash chromatography (PE/
Et2O, 80:20), the cyclopentenone 4hf as a yellow oil (1.03 g, 74%):
3
3
1.57 [sextet, J = 7.3 Hz, 2 H, (C-2)CH2CH2], 0.86 (t, J = 7.3 Hz,
3 H, CH3) ppm. MS (EI): m/z (%) = 212 (99) [M]+, 197 (23) [M+
–
CH3], 183 (50) [M+ – C2H5], 169 (59) [M+ – C3H7], 155 (78), 153
(52), 141 (42), 129 (38), 128 (44), 115 (100), 91 (39), 77 (43) [Ph+],
69 (29), 63 (35), 51 (34), 41 (28), 39 (57), 27 (42).
R = 0.33 (PE/Et O, 80:20). IR (thin film): ν = 2960, 2920, 2860,
˜
f
2
5ec: Yellow oil; R = 0.37 (PE/Et O, 85:15). IR (thin film): ν =
˜
f
2
1700 (C=O), 1650, 1580, 1450, 1200, 990, 920, 880, 850 cm–1. H
1
3080, 3060, 3020, 2960, 2920, 2860, 1710 (C=O), 1640, 1600, 1500,
NMR (300 MHz, CDCl3): δ = 7.72 (s, 1 H, 3-H), 2.92 (s, 2 H, 5-
1
1450, 1380, 1190, 1060, 910, 740, 700 cm–1. H NMR (300 MHz,
3
H), 2.38 (m, 2 H, C=CCH2), 2.24 [t, J = 7.7 Hz, 2 H, (C-2)CH2],
CDCl3): δ = 7.60 (s, 1 H, 3-H), 7.34–7.24 (m, 3 H, 2ϫ Hm and 1ϫ
2.19 (m, 2 H, C=CCH2), 1.60 (m, 6 H, 3ϫ CH2), 1.55–1.45 (m, 2
3
4
Hp), 7.14 (dd, Jo = 8.1, Jm = 1.5 Hz, 2 H, 2ϫ Ho), 5.39 [br. s, 1
H, (C-4)=CHtrans], 5.05 [br. s, 1 H, (C-4)=CHcis], 4.01 (s, 1 H, 5-
3
H, CH2), 1.33–1.27 (m, 4 H, 2ϫ CH2), 0.88 (t, J = 6.8 Hz, 3 H,
CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 206.4 (C-1, C=O),
150.5 (C-3), 146.1 (C-2), 138.9 [(C-4)=C(CH2)5], 127.0 (C-4), 39.0
(C-5), 32.9, 31.7, 30.4, 28.1, 27.8, 27.7, and 25.0 (7ϫ CH2), 26.5
(CH2C-CO), 22.5 (CH3CH2), 14.0 (CH3) ppm. MS (EI): m/z (%) =
232 (100) [M]+, 203 (31) [M+ – C2H5], 189 (66) [M+ – C3H7], 176
(61), 175 (26) [M+ – C4H9], 133 (26), 108 (26), 90 (50), 79 (39), 77
3
3
H), 2.31 [t, J = 7.3 Hz, 2 H, (C-2)CH2], 1.60 [sextet, J = 7.3 Hz,
2 H, (C-2)CH2CH2], 0.97 (t, 3J = 7.3 Hz, 3 H, CH3) ppm. MS (EI):
m/z (%) = 212 (99) [M]+, 197 (19) [M+ – CH3], 183 (42) [M+
–
C2H5], 169 (53) [M+ – C3H7], 155 (84), 153 (47), 141 (40), 128 (44),
115 (100), 91 (43), 77 (33) [Ph+], 39 (39), 27 (33).
2-Propyl-4-[(trimethylsilyl)methylene]cyclopent-2-enone
(4ed): (38), 67 (26), 41 (50). C16H24O (232.37): calcd. C 80.70, H 10.41;
(Table 6, entry 9) Following procedure B, cycloaddition of the (1-
pentyne)hexacarbonyldicobalt complex (2e; 230 mg, 0.65 mmol)
with trimethylsilylallene (3d; 109 mg, 0.97 mmol) promoted by
NMO (457 mg, 3.9 mmol) in CH2Cl2/THF (1:1, 8 mL) gave, after
flash chromatography (PE/Et2O, 90:10), the cyclopentenones (E)-
4ed (77 mg, 50%) and (Z)-4ed (7 mg, 4%).
found C 80.53, H 10.44.
4-Cyclohexylidene-2-phenylcyclopent-2-enone (4ff): (Scheme 3) Fol-
lowing procedure B, cycloaddition of the (phenylacetylene)hexacar-
bonyldicobalt complex (2f; 776 mg, 2 mmol) with vinylidenecyclo-
hexane (3f; 260 mg, 2.4 mmol) promoted by NMO (1.405 g,
12 mmol) in CH2Cl2/THF (1:1, 12 mL) gave, after flash chromatog-
raphy (PE/Et2O, 80:20), the cyclopentenone 4ff as a yellow oil
(E)-4ed: Yellow oil; R = 0.35 (PE/Et O, 92:8). IR (neat): ν = 2960,
˜
f
2
1710 (C=O), 1610, 1380, 1250, 1040, 930, 840, 690 cm–1. 1H NMR (318 mg, 67%): R = 0.34 (PE/Et O, 80:20). IR (thin film): ν =
˜
f
2
(300 MHz, CDCl3): δ = 7.27 (s, 1 H, 3-H), 5.81 [s, 1 H, (C-4)=CH- 3030, 2960, 2920, 2860, 1690 (C=O), 1650, 1600, 1580, 1490, 1450,
SiMe3], 2.95 (s, 2 H, 5-H), 2.21 [t, 3J = 7.3 Hz, (C-2)CH2], 1.50 1350, 1290, 1270, 1130, 920, 770, 730, 690 cm–1. 1H NMR
Eur. J. Org. Chem. 2010, 3312–3336
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3331

F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
3
4
3
3
4
(300 MHz, CDCl3): δ = 8.23 (s, 1 H, 3-H), 7.82 (dd, Jo = 8.3, Jm 6.62 [t, J = 7.4 Hz, 1 H, (C-5)=CHCH2], 6.38 (dt, J = 5.9, J =
3
= 1.3 Hz, 2 H, 2ϫ Ho), 7.41–7.26 (m, 3 H, 2ϫ Hm and 1ϫ Hp),
3.12 (s, 2 H, 5-H), 2.48 [m, 2 H, (C-4)=CCH2], 2.26 [m, 2 H, (C-
4)=CCH2], 1.65 (m, 6 H, 3ϫ CH2) ppm. 13C NMR (75 MHz,
2.2 Hz, 1 H, 2-H), 3.19 [br. s, 1 H, (C-4)H2], 2.21 [q, J ≈ 7.4 Hz,
2 H, (C-5)=CHCH2], 1.53–1.21 (m, 8 H, 4ϫ CH2), 0.88 (t, 3J =
7.0 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 196.6
CDCl3): δ = 204.3 (C-1, C=O), 150.3 (C-3), 142.5 (C-2), 141.0 [(C- (C-1, C=O), 158.9 (C-3), 136.22 and 136.20 [C-2 and/or (C-5)
4)=C(CH2)5], 132.2 [C(Ph)i], 128.5 [2ϫ CH(Ph)m], 128.2 [CH-
(Ph)p], 127.1 [2ϫ CH(Ph)o], 126.8 (C-4), 40.3 (C-5), 33.2, 30.6,
28.3, 27.9 and 26.5 (5ϫ CH2) ppm. HRMS (EI): calcd. for
C17H18O [M]+ 238.1358; found 238.1350.
C=CH], 134.0 (C-5), 32.1 (C-4), 31.7, 29.7, 29.0 and 28.4 (4ϫ
CH2), 22.6 (CH2CH3), 14.0 (CH3) ppm. MS (EI): m/z (%) = 178
(10) [M]+, 121 (33), 95 (100), 91 (22), 82 (78), 79 (47), 77 (57), 55
(60), 53 (22), 43 (29), 40 (48), 39 (31).
4-Heptylidenecyclopent-2-enone (4ab): (Table 7, entry 1) Following
procedure B, after warming up the reaction mixture over 1 h and
stirring at r.t. for 15 h, the cycloaddition of the acetylene-hexacar-
bonyldicobalt complex (2a; 468 mg, 1.5 mmol) with nona-1,2-diene
(3b; 280 mg, 2.25 mmol) promoted by NMO (1.054 g, 9 mmol) in
CH2Cl2/THF (1:1, 16 mL) afforded, after flash chromatography
(PE/Et2O, 75:25), the cyclopentenone 4ab as an inseparable mixture
of E and Z stereoisomers (139 mg, 52%, E/Z = 78:22), the cyclo-
pentenone 5ab (13 mg, 5%), the 5-alkylidenecyclopentenone (E)-
6ab (37 mg, 14%), and the tricyclic diketone 10b (30 mg, 11%).
3,5-Diheptyl-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene-1,8-dione
(10b): R = 0.20 (PE/Et O, 70:30). IR (thin film): ν = 2960, 2920,
˜
f
2
2850, 1790 (C=O of bridge), 1700 (conjugated C=O), 1610, 1460,
1
4
1380, 1180 cm–1. H NMR (300 MHz, CDCl3): δ = 6.06 (dt, J =
1.4, 4J = 1.4 Hz, 1 H, 2-H), 5.96 (dt, J = 3.4, J = 1.5 Hz, 1 H, 6-
H), 3.40 (ddd, 3J = 6.2, 3J = 4.5, 4J = 1.4 Hz, 1 H, 3a-H), 3.32
(ddd, 3J = 5.0, 3J = 3.4, 4Jw = 1.5 Hz, 1 H, 7-H), 3.10 (dd, 3J =
3
4
4
3
3
4.5, Jw = 1.5 Hz, 1 H, 4-H), 2.92 (dd, J = 6.2, J = 5.0 Hz, 1 H,
3
4
7a-H), 2.32 [dt, J = 7.0, J = 1.4 Hz, 2 H, (C-3)CH2], 1.99 [m, 2
H, (C-5)CH2], 1.52–1.20 (m, 20 H, 10ϫ CH2), 0.87 (t, 3J = 7.0 Hz,
6 H, 2ϫ CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 206.7 (C-
8), 198.6 (C-1), 179.7 (C-3), 143.4 (C-5), 135.2 (CH-2), 121.7 (CH-
6), 52.6, 49.6, 45.2 and 43.4 (4ϫ CH), 32.6, 31.9, 31.8, 31.7, 31.6,
29.7, 29.3, 29.1, 29.0, 26.8, 26.1 and 22.6 (12ϫ CH2), 14.0 and 14.0
(2ϫ CH3) ppm.
Alternatively, following procedure B (Table 7, entry 3), after 4 h,
the cycloaddition of the acetylene-hexacarbonyldicobalt complex
(2a; 156 mg, 0.5 mmol) with nona-1,2-diene (3b; 93 mg, 0.75 mmol)
promoted by NMO (351 mg, 3 mmol) in CH2Cl2/THF (1:1, 6 mL)
gave, after flash chromatography (PE/Et2O, 75:25), the cyclopen-
tenones 4ab (E/Z = 73:27), 5ab and (E)-6ab (70 mg, 79%, with a
90:3:7 ratio determined by GC analysis).
4-Benzylidenecyclopent-2-enone (4ac):[31a] (Table 7, entry 5) Follow-
ing procedure B, after 4 h, the cycloaddition of the acetylene-hexa-
carbonyldicobalt complex 2a (5.39 g, 17.3 mmol) with phenylallene
3c (2.72 g, 23.4 mmol) promoted by NMO (12.18 g, 104 mmol) in
CH2Cl2/THF (1:1, 140 mL), gave a crude oil (GC analysis: 4ac/
5ac/6ac = 77:5:18). Purification by flash chromatography (PE/Et2O,
60:40) gave the cyclopentenone (E + Z)-4ac (673 mg, 23%, E/Z =
86:14), the cyclopentenone 5ac (41 mg, 1%), and the 5-alkylidene-
cyclopentenone (E)-6ac (yellow solid, 112 mg, 4%). Pure (E)-4ac
was isolated after a second flash chromatographic column.
4ab (E and Z): Yellow oil; Rf = 0.37 (PE/Et2O, 70:30). UV/Vis
(EtOH): λmax (ε, Lmol–1 cm–1) (E + Z): 283 (17105) nm. IR (neat):
ν (E + Z) = 2960, 2920, 2850, 1710 (C=O), 1610, 1540, 1460, 1180,
˜
1160, 1070, 780 cm–1.
1
3
(E)-4ab: H NMR (300 MHz, CDCl3): δ = 7.66 (d, J = 5.5 Hz, 1
3
3
H, 3-H), 6.15 (d, J = 5.5 Hz, 1 H, 2-H), 5.77 [t, J = 7.7 Hz, 1 H,
(C-4)=CHCH2], 2.85 (s, 2 H, 5-H), 2.12 [q, J ≈ 7.4 Hz, 2 H, (C-
4)=CHCH2], 1.44–1.23 (m, 8 H, 4ϫ CH2), 0.84 (t, J = 6.6 Hz, 3
3
3
H, CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 206.3 (C-1,
C=O), 160.5 (C-3), 137.5 (C-4), 132.7 and 131.7 [C-2 and/or (C-
4)=CH], 37.2 (C-5), 31.6, 30.1, 28.9 and 28.8 (4ϫ CH2), 22.5
(CH2CH3), 14.0 (CH3) ppm.
(E + Z)-4ac: Yellow solid; Rf = 0.23 (PE/Et2O, 60:40). IR (KBr
disc): ν = 3095, 3065, 3025, 2970, 2910, 1705 (C=O), 1670, 1535,
˜
1495, 1445, 1395, 1355, 1235, 1195, 1155, 1080, 930, 915, 890, 835,
825, 790, 750, 700, 685, 645, 620 cm–1.
1
3
1
3
(E)-4ac: H NMR (300 MHz, CDCl3): δ = 7.88 (d, J = 5.5 Hz, 1
H, 3-H), 7.47–7.28 (m, 5 H, 5ϫ ArH), 6.68 [s, 1 H, (C-4)=CH-Ph],
(Z)-4ab: H NMR (300 MHz, CDCl3): δ = 8.00 (d, J = 5.5 Hz, 1
3
5
3
H, 3-H), 6.22 (dd, J = 5.5, J = 1.5 Hz, 1 H, 2-H), 5.66 [t, J =
7.9 Hz, 1 H, (C-4)=CHCH2], 2.91 (s, 2 H, 5-H), 2.27 [q, 3J ≈
7.4 Hz, 2 H, (C-4)=CHCH2], 1.44–1.23 (m, 8 H, 4ϫ CH2), 0.84 (t,
3J = 6.6 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ =
206.9 (C-1, C=O), 154.7 (C-3), 135.7 (C-4), 133.8 (C-2), 130.4 [(C-
4)=CH], 40.0 (C-5), 31.6, 29.5, 28.8 and 28.4 (4ϫ CH2), 22.5
(CH2CH3), 14.0 (CH3) ppm. GC–MS (EI): m/z (%) (E)-4ab = 178
(27) [M]+, 107 (15) [M+ – C5H11], 95 (26), 94 (100), 79 (17), 77 (24),
66 (17), 55 (11), 43 (14), 41 (16), 39 (11). GC–MS (EI): m/z (%)
(Z)-4ab = 178 (25) [M]+, 107 (14) [M+ – C5H11], 95 (27), 94 (100),
79 (23), 77 (25), 66 (20), 55 (13), 43 (14), 41 (16), 39 (10).
3
6.30 (d, J = 5.5 Hz, 1 H, 2-H), 3.27 (s, 2 H, 5-H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 206.3 (C-1, C=O), 162.4 (C-3), 137.7 and
136.2 [C-4 and/or C(Ph)i], 132.7 (C-2), 129.3 [2ϫ CH(Ph)o], 129.2
[CH(Ph)p], 128.9 [2ϫ CH(Ph)m], 128.5 [(C-4)=CHPh], 39.4 (C-5)
ppm. MS (ESI): (E + Z 4ac): m/z = 193 [M + Na]+, 171 [M +
H]+, 153 [(M + H)+ – H2O].
1
3
(Z)-4ac: H NMR (300 MHz, CDCl3): δ = 8.24 (d, J = 5.7 Hz, 1
H, 3-H), 7.47–7.28 (m, 5 H, 5ϫ ArH), 6.72 [s, 1 H, (C-4)=CHPh],
3
5
6.41 (dd, J = 5.5, J = 1.8 Hz, 1 H, 2-H), 3.17 (s, 2 H, 5-H) ppm.
13C NMR (75 MHz, CDCl3): δ = 206.0 (C-1, C=O), 155.5 (C-3),
137.3 [C-4 or C(Ph)i], 136.4 (C-2), 136.3 [C-4 or C(Ph)i], 128.8,
128.5, 128.2 and 128.1 [5ϫ CH(Ph) and (C-4)=CHPh], 41.5 (C-5)
5ab: R = 0.46 (PE/Et O, 70:30). IR (neat): ν = 2960, 2920, 2850,
˜
f
2
1710 (C=O), 1610, 1540, 1460, 1180, 1160, 1070, 780 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 7.73 (d, 3J = 5.5 Hz, 1 H, 3-H), 6.27
(dd, 3J = 5.5, 5J = 1.1 Hz, 1 H, 2-H), 5.40 [d, 4J = 0.7 Hz, 1 H,
ppm. The H and 13C NMR spectroscopic data were in full agree-
1
ment with those reported in the literature for (E)-5ac and (Z)-
5ac.[31a]
3
(C-4)=CHcis], 5.29 [br. s, 1 H, (C-4)=CHtrans], 2.81 (t, J = 5.7 Hz,
1 H, 5-H), 1.61 [m, 2 H, (C-4)=CHCH2], 1.48–1.25 (m, 8 H, 4ϫ
CH2), 0.88 (t, 3J = 6.8 Hz, 3 H, CH3) ppm. MS (EI): m/z (%) =
178 (6) [M]+, 95 (14), 94 (100), 77 (16), 41 (17).
5ac: Yellow oil; R = 0.30 (PE/Et O, 60:40). IR (neat): ν = 2940,
˜
f
2
2900, 2840, 1700 (C=O), 1490, 1460, 1445, 1370 cm–1. 1H NMR
3
(300 MHz, CDCl3): δ = 7.92 (d, J = 5.6 Hz, 1 H, 3-H), 7.40–7.10
3
(E)-6ab: R = 0.27 (PE/Et O, 70:30). IR (neat): ν = 2960, 2920,
(m, 5 H, 5ϫ ArH), 6.36 (d, J = 5.6 Hz, 1 H, 2-H), 5.54 [s, 1 H,
˜
f
2
2850, 1700 (C=O), 1460, 1380, 1260, 740 cm–1. 1H NMR
(C-4)=CHcis], 5.20 [s, 1 H, (C-4)=CHtrans], 3.99 (s, 1 H, 5-H) ppm.
3
3
(300 MHz, CDCl3): δ = 7.57 (dt, J = 5.9, J = 2.9 Hz, 1 H, 3-H),
13C NMR (75 MHz, CDCl3): δ = 206.5 (C-1, C=O), 159.8 (C-3),
3332
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 3312–3336

Pauson–Khand Reaction of Allenic Hydrocarbons
149.9 (C-4), 137.2 [C(Ph)i], 133.9 (C-2), 129.2 [2ϫ CH(Ph)o], 128.9 NMO (2.8 mg, 24 mmol) in CH2Cl2/THF (50 mL) gave, after 4 h
[2ϫ CH(Ph)m], 127.6 [CH(Ph)p], 115.6 [(C-4)=CH2], 55.6 (C-5)
ppm.
reaction time followed by purification by flash chromatography
(PE/Et2O, 20:80), the tricyclic diketones 10a (85 mg, 22%) and 11a
(26 mg, 7%).
(E)-6ac: Yellow solid; R = 0.20 (PE/Et O, 60:40). IR (KBr disc): ν
˜
f
2
= 3060, 3030, 2925, 2855, 1690 (C=O), 1630, 1495, 1450, 1405,
1340, 1290, 1270, 1225, 1185, 1080, 1030, 945, 840, 790, 760, 740,
690, 635 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.71–7.66 (dtd,
3,5-Dimethyl-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene-1,8-dione
(10a):[74] Yellow oil; R = 0.36 (PE/Et O, 20:80). IR (neat): ν =
˜
f
2
2920, 1780 (C=O of bridge), 1690 (conjugated C=O), 1610, 1440,
3
5
3
4
3J = 5.9, J = 2.4, J = 0.9 Hz, 1 H, 3-H), 7.59 (dd, Jo = 7.8, Jm
1380, 1300, 1280, 1190, 1090, 910, 880, 820, 710 cm–1. 1H NMR
4
= 1.4 Hz, 2 H, 2ϫ Ho), 7.46–7.30 [m, 4 H, 2ϫ Hm, Hp and (C-
(300 MHz, CDCl3): δ = 6.00 (q, J = 2.5 Hz, 1 H, 2-H), 5.89 (dq,
4
5)=CHPh], 6.48 (dt, 3J = 5.9, J = 2.1 Hz, 1 H, 2-H), 3.58 (ddd, 3J
4
3
3
3J = 4.9, J = 3.0 Hz, 1 H, 6-H), 3.29 (dd, J = 5.3, J = 5.0 Hz, 1
4
4
= 2.4, J = 2.1, J = 2.1 Hz, 2 H, 4-H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 197.9 (C-1, C=O), 157.5 (C-3), 135.9 [(C-5)=CHPh],
135.6 [C(Ph)i], 132.7 (C-5), 132.4 (CH-2), 130.8 [2ϫ CH(Ph)o],
129.9 [CH(Ph)p], 129.3 [2ϫ CH(Ph)m], 34.7 (CH2-4) ppm.
3
3
3
H, 7a-H), 3.20 (dd, J = 5.0, J = 4.9 Hz, 1 H, 7-H), 3.01 (d, J =
4.4 Hz, 1 H, 4-H), 2.83 (dd, 3J = 5.3, 3J = 4.4 Hz, 1 H, 3a-H), 2.05
4
4
[d, J = 2.5 Hz, 3 H, (C-3)CH3], 1.69 [d, J = 3.0 Hz, 3 H, (C-5)
CH3] ppm. 13C NMR (75 MHz, CDCl3): δ = 206.6 (C-8, C=O),
198.5 (C-1, C=O), 174.8 (C-3), 138.7 (C-5), 136.7 (CH-2), 122.9
(CH-6), 53.2, 50.0, 45.4 and 44.5 (4ϫ CH), 18.4 and 18.1 (2ϫ
CH3) ppm. MS (EI): m/z (%) = 160 (29) [M+ – CO], 150 (100), 117
(26), 115 (28), 91 (36), 68 (20), 65 (18), 40 (31), 39 (27).
4-Cyclohexylidenecyclopent-2-enone (4af): (Table 8, entry 3) Follow-
ing procedure C, cycloaddition of the acetylene-hexacarbonyldico-
balt complex 2a (312 mg, 1.0 mmol) with vinylidenecyclohexane 3f
(162 mg, 1.5 mmol) promoted by NMO (703 mg, 6 mmol) in
CH2Cl2/THF (1:1, 10 mL) gave, after flash chromatography (PE/
Et2O, 60:40), the cyclopentenone 4af (83 mg, 46%) and 5-cyclohex-
ylidenecyclopent-2-enone 6af (21 mg, 18%).
3,6-Dimethyl-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene-1,8-dione
(11a): Yellow oil; R = 0.42 (PE/Et O, 20:80). IR (neat): ν = 2920,
˜
f
2
1780 (C=O of bridge), 1690 (conjugated C=O), 1610, 1440, 1380,
1300, 1280, 1190, 1090, 910, 880, 820, 710 cm–1. 1H NMR
4af: Yellow oil; R = 0.34 (PE/Et O, 60:40). IR (neat): ν = 2960,
˜
f
2
3
4
(300 MHz, CDCl3): δ = 6.06 (s, 1 H, 2-H), 5.73 (dd, J = 4.4, J =
1.1 Hz, 1 H, 5-H), 3.30 (dd, 3J = 5.5, 3J = 5.2 Hz, 1 H, 7a-H), 3.18
2920, 2850, 1700 (C=O), 1670, 1600, 1530, 1450, 1390, 1190, 1170,
920, 860, 850, 800 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.05 (d,
3
3
3
(dd, J = 5.5, J = 4.4 Hz, 1 H, 4-H), 3.14 (d, J = 5.2 Hz, 1 H, 7-
3
3J = 5.5 Hz, 1 H, 3-H), 6.15 (d, J = 5.5 Hz, 1 H, 2-H), 2.87 (s, 2
3
H), 2.93 (t, J = 5.5 Hz, 1 H, 3a-H), 2.03 [s, 3 H, (C-3)CH3], 1.79
H, 5-H), 2.37 [m, 2 H, (C-4)=CCH2], 2.19 [m, 2 H, (C-4)=CCH2],
1.59 (m, 6 H, 3ϫ CH2) ppm. 13C NMR (75 MHz, CDCl3): δ =
207.1 (C-1, C=O), 155.9 (C-3), 142.5 (C-4), 132.6 (C-2), 128.7 [(C-
4)=C], 38.5 (C-5), 33.1, 30.5, 28.2, 27.7 and 26.4 (5ϫ CH2) ppm.
HRMS (EI): calcd. for C11H14O [M]+ 162.1045; found 162.1042.
[d, 4J = 1.1 Hz, 3 H, (C-6)CH3] ppm. 13C NMR (75 MHz, CDCl3):
δ = 205.8 (C-8, C=O), 198.6 (C-1, C=O), 175.7 (C-3), 141.4 (C-6),
136.8 (CH-2), 120.4 (CH-5), 53.3, 49.9, 45.9 and 44.7 (4ϫ CH),
18.2 and 18.1 (2ϫ CH3) ppm. MS (EI): m/z (%) = 160 (34) [M+
–
CO], 15 (100), 117 (26), 115 (32), 91 (38), 68 (15), 65 (15), 40 (21),
39 (19).
6af: Yellow oil; R = 0.44 (PE/Et O, 60:40). IR (thin film): ν =
˜
f
2
2960, 2920, 2850, 1700 (C=O), 1670, 1600, 1530, 1450, 1390, 1190,
1170, 920, 860, 850, 800 cm–1. 1H NMR (300 MHz, CDCl3): δ =
3
3
3
4
Acknowledgments
7.40 (dt, J = 5.9, J = 2.8 Hz, 1 H, 3-H), 6.31 (dt, J = 5.9, J =
3
4
2.0 Hz, 1 H, 2-H), 3.18 [dd, J = 2.8, J = 2.0 Hz, 2 H, H-4], 3.06
[app t, 3J = 6.2 Hz, 2 H, (C-5)=C(CH2)cis], 2.23 [app t, 3J = 6.2 Hz,
2 H, (C-5)=C(CH2)trans], 1.70–1.60 (m, 6 H, 3ϫ CH2) ppm.
Two of us (F. A. and S. L.) gratefully acknowledge Ministry of Su-
perior Education and Research (MESR) for PhD grants. The au-
thors thank B. Fenet for helpful assistance in the analysis of NMR
spectra. They also gratefully acknowledge the CINES/GENCI for
computer time (Project cpt2130).
6,7,8,9,10,10a-Hexahydro-1(5H)-cyclopentacyclononenone
(4ah):
(Scheme 5) Following procedure B, after 6 h, the cycloaddition of
the acetylene-hexacarbonyldicobalt complex 2a (1.21 g, 3.84 mmol)
with cyclonona-1,2-diene 3h (709 mg, 5.8 mmol) promoted by
NMO (2.7 g, 23.04 mmol) in CH2Cl2/THF (1:1, 20 mL) gave, after
flash chromatography (PE/Et2O, 70:30), the cyclopentenone 4ah
(402 mg, 59%).
[1] a) I. U. Khand, P. L. Pauson, W. E. Watts, J. Chem. Soc.,
Chem. Commun. 1971, 36; b) I. U. Khand, G. R. Knox, P. L.
Pauson, W. E. Watts, M. I. Foreman, J. Chem. Soc. Perkin
Trans. 1 1973, 977–981.
4ah: Yellow oil; R = 0.35 (PE/Et O, 70:30). IR (neat): ν = 2920,
˜
f
2
[2] For reviews, see: a) N. Jeong, Comprehensive Organometallic
Chemistry III, (Eds.: R. H. Crabtree, D. M. P. Mingos), Elsev-
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2850, 1700 (C=O), 1550, 1470, 1440, 1350, 1240, 1160, 1080, 940,
870, 830, 820, 790 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.71 (d,
3
3J = 5.5 Hz, 1 H, 3-H), 6.12 (d, J = 5.5 Hz, 1 H, 2-H), 5.82 (dd,
3
3
3
3J = 11.5, J = 6.3 Hz, 1 H, 4-H), 2.72 (dd, J = 9.1, J = 3.4 Hz,
1 H, 10a-H), 2.46 (m, 1 H, 5-H), 2.38 (m, 1 H, 5Ј-H), 2.28 (m, 1
H, 10-H), 1.87 (m, 1 H, 10Ј-H), 1.60–1.70 (m, 4 H, 2ϫ CH2), 1.37–
1.60 (m, 4 H, 2ϫ CH2) ppm. 13C NMR (75 MHz, CDCl3): δ =
209.8 (C-1, C=O), 160.9 (C-3), 144.6 (C-3a), 131.6 (C-2), 130.6 [C-
4, (C-3a)=CH], 49.6 (C-10a), 30.1, 29.0, 28.2, 27.7, 26.7 and 22.2
(6ϫ CH2) ppm. MS (EI): m/z (%) = 176 (58) [M]+, 133 (19), 107
(25), 105 (25), 95 (31), 94 (46), 91 (86), 81 (58), 79 (65), 77 (64), 67
(58), 65 (51), 55 (71), 53 (49), 51 (41), 41 (100), 39 (84), 27 (50).
Tricyclic Diketones 10a and 10b: (Scheme 6) Following procedure
B (as for cyclopentenone 4da, Table 3, entry 2), cycloaddition of the
acetylene-hexacarbonyldicobalt complex 2a (1.25 g, 4 mmol) with
propadiene (condensed at –78 °C, 1 mL, 17 mmol) promoted by
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Habib, J. Chem. Res., Miniprint 1977, 4418–4433; c) I. U.
Khand, P. L. Pauson, J. Chem. Res., Synop. 1977, 9; d) I. U.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3335

F. Antras, S. Laurent, M. Ahmar, H. Chermette, B. Cazes
FULL PAPER
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