PtCl2-mediated cycloisomerization of unsaturated propargylic carboxylates

Article abstract of DOI:10.1016/j.tet.2005.03.019

The PtCl₂-mediated cycloisomerization of unsaturated propargylic carboxylates yields differently functionalized bicyclo[4.1.0]heptane enol esters from moderate to good yield, in a very diastereoselective manner. We have prepared and submitted to PtCl₂-catalyzed cycloisomerization a series of differently substituted hept-1-en-6-ynes with different O-acyl (acetyl, trichloroacetyl, 3,4,5-trimethoxybenzoyl, etc.) protecting groups at propargylic positions, investigating also the effect of the geometry at the double bond, as well as the effect of the number of substituents at the alkene moiety. As a result, we have found that the O-acetyl migrating group is the best one in terms of simplicity and chemical yields. In this reaction we have isolated mixtures of compounds formed by minor 1-acetoxy-allenes and major bicyclo[4.1.0]heptane derivatives. Major products are the result of a sequential process involving steps of cycloisomerization plus cyclopropanation, followed by acyl migration. The basic methanolysis (K₂CO₃, MeOH) of these intermediates gave mixtures of cis and trans-caran-2-ones. This two-step protocol (cycloisomerization plus basic methanolysis) for the syntheses of α,β-unsaturated cyclopropyl ketones constitutes a synthetic alternative to the usual unfriendly, intramolecular cyclopropanation of unsaturated α-diazocarbonyl derivatives. The formation of these bicyclo[4.1.0]heptane derivatives is a simple, but efficient entry into the skeleton of the 'carane' family of natural products.

Full text of DOI:10.1016/j.tet.2005.03.019

Tetrahedron 61 (2005) 4793–4803
PtCl2-mediated cycloisomerization of unsaturated
propargylic carboxylates
*
´
Shazia Anjum and Jose Marco-Contelles
Laboratorio de Radicales Libres, IQOG (CSIC), C/Juan de la Cierva 3, 28006 Madrid, Spain
Received 11 January 2005; revised 22 February 2005; accepted 4 March 2005
Available online 7 April 2005
Abstract—The PtCl2-mediated cycloisomerization of unsaturated propargylic carboxylates yields differently functionalized bicyclo[4.1.0]-
heptane enol esters from moderate to good yield, in a very diastereoselective manner. We have prepared and submitted to PtCl2-catalyzed
cycloisomerization a series of differently substituted hept-1-en-6-ynes with different O-acyl (acetyl, trichloroacetyl, 3,4,5-trimethoxy-
benzoyl, etc.) protecting groups at propargylic positions, investigating also the effect of the geometry at the double bond, as well as the effect
of the number of substituents at the alkene moiety. As a result, we have found that the O-acetyl migrating group is the best one in terms of
simplicity and chemical yields. In this reaction we have isolated mixtures of compounds formed by minor 1-acetoxy-allenes and major
bicyclo[4.1.0]heptane derivatives. Major products are the result of a sequential process involving steps of cycloisomerization plus
cyclopropanation, followed by acyl migration. The basic methanolysis (K2CO3, MeOH) of these intermediates gave mixtures of cis and
trans-caran-2-ones. This two-step protocol (cycloisomerization plus basic methanolysis) for the syntheses of a,b-unsaturated cyclopropyl
ketones constitutes a synthetic alternative to the usual unfriendly, intramolecular cyclopropanation of unsaturated a-diazocarbonyl
derivatives. The formation of these bicyclo[4.1.0]heptane derivatives is a simple, but efficient entry into the skeleton of the ‘carane’ family of
natural products.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
cycloisomerization plus cyclopropanation reactions,
respectively, while products of type C were the formal
result of a cycloisomerization and cyclopropanation
followed by acyl migration, both transformations involving
possibly Pt cyclopropyl carbenes. More recently Malacria
and co-workers have reported the PtCl2-catalyzed cyclo-
isomerization of 5-en-1-yn-3-ol systems,4b as well as the
tandem PtCl2 catalyzed-thermal [3,3] rearrangements of
enyne acetates.4c
Transition-metal catalyzed cycloisomerization of 1,6-
enynes1 constitutes one of the best known examples of
what has been called ‘full atom economy’ reactions.2
Particularly attractive has been the use of the readily
available and stable platinum salts and complexes as
catalysts. Since the pioneer work by Trost,3a–c a number
of reports from different laboratories have highlighted the
mechanism of these isomerizations, as well as the scope and
limitations of this synthetic procedure for the preparation of
carbocycles and/or heterocycles.3,4 In this context,
Fensterbank, Malacria and Marco-Contelles4a have reported
the critical effect that the type of the substituents at
propargylic positions in differently functionalized 1,6-
enynes have on the course of their PtCl2-mediated
cycloisomerization reactions. It was noticed that on
going from the free alcohol (or ethers) to O-acyl derivatives
the major final resulting products were completely
different (Scheme 1).4a Compounds of type A and B were
obtained after skeletal rearrangement, and sequential
Scheme 1.
Keywords: Propargylic carboxylates; PtCl2-mediated cycloisomerization;
Hept-1-en-6-ynes; Cyclopropanes; Bicyclo[4.1.0]heptanes; Carane natural
products.
A careful revision of the current literature has shown that
this attractive PtCl2-mediated cycloisomerization reaction4a
has precedent on a work published by Ohloff et al. some
*
Corresponding author. Tel.: C34 91 562 29 00; fax: C34 91 564 48 53;
e-mail: iqoc21@iqog.csic.es
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.03.019

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S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
unsaturated double bond with the quaternary center, and
moving the gem-dimethyl groups at the allylic position to
the terminal carbon of the alkene moiety. Then, compounds
1–6, incorporating different acyloxy groups to operate in the
presumed key isomerization process, were designed. These
precursors were readily prepared in two steps, after
Grignard reaction of commercial 6-methyl-5-heptene-2-
one with ethynylmagnesium bromide, followed by O-acyla-
tion of the resulting 3,7-dimethyl-oct-6-en-1-yn-3-ol6a
(Schemes 2 and 3).
Scheme 2. Reagents: (a) Ac2O, py, DMAP, rt, 12 h [(1): XZCOCH3,
81%]. (b) (Cl3CCO)2O, py, DMAP, rt, 45 min [(2): XZCOCCl3, 79%].
(c) C6H5COCl, py, DMAP, reflux, 46 h [(3): XZCOC6H5, 64%].
(d) C6H2(OCH3)3COCl, py, DMAP, reflux, 24 h {(4): XZCO[3,4,5-
(OCH3)3C6H2], 49%}. (e) 4-(NO2)C6H4COCl, py, DMAP, 80 8C, 16 h [(5):
XZCO[4-(NO2)C6H4], 70%].
Precursor 1,6a under the standard conditions [PtCl2 (5%),
toluene, 40 8C], afforded the known 1-acetoxy allene 76a,7
and the bicyclo[4.1.0]heptane enol acetate 85a (Table 1,
entry a). Compound 8 has been already described in
literature5a and the reported spectroscopic data are in good
agreement with the ones that we have observed in our
sample. The formation of the allenyl esters has not been
detected in our previous experiments,4a but they are
routinely found in the transition metal-catalyzed isomeriza-
tion of propargylic acetates.8 However, it has been reported
that heating propargylic acetates in benzene or toluene with
PtCl2 or silver trifluoroacetate as catalyst gives a diene type
of product, instead of the allenyl acetate, the product
obtained with copper chloride as catalyst.7b Very interest-
ingly, compound 1, without catalyst, at 60 8C for 72 h, in
toluene as solvent, was recovered unreacted, and when
PdCl2 (5% mol) was used as catalyst, no reaction was
observed at 40 8C for 15 h, or after 44 h at 80 8C. Using gold
trichloride (AuCl3), in the same conditions, we were able to
isolate compounds 7 and 8 in 33 and 29% yields,
respectively. Regarding the solvent, with PtCl2 as catalyst,
in methylene chloride, only product 8 was isolated in 25%,
after 70 h at 40 8C.
Scheme 3. Reagents: (a) Ethynylmagnesium bromide, 2 h, rt; then
ClCO2Et, py, DMAP, 5 h, rt (68%).
years ago.5a In 1984 Rautenstrauch described the same
reaction,5b and found that from related precursors, but using
PdCl2(CH3CN)2 as catalyst, similar products were obtained
in better yields (10–40%). After this preliminary communi-
cation, no further reports from this laboratory were
available, and the potential interest of this new mode of
cycloisomerization reaction, as well as the potential
synthetic applications of the resulting building blocks,
remained unexplored until was have rediscovered it by
serendipity (Scheme 1).4a Ohe and Uemura have recently
reported the intermolecular version5c of this reaction.
2. Results and discussion
Trichloroacetate 2, under the standard conditions for the
cycloisomerization reaction, gave a complex reaction
mixture, in a very slow reaction. After work-up and
isolation, only product 9 was isolated in poor yield (20%)
(Table 1, entry b). This result shows the importance of the
anchimeric assistance of the acyloxy group at the
propargylic position for the success of this process. Very
clearly, the efficiency of the cycloisomerization reaction
was hampered by the low anchimeric assistance ability of
The unexplored and high synthetic potential of these results
led us to start a research program aimed at establishing the
scope and generality of the PtCl2-catalyzed cycloisomeriza-
tion of unsaturated propargylic carboxylates. In order to do
this, we have prepared new 1,6-enyne derivatives, simplify-
ing the structure of our former precursors, with a methyl
substituent at the quaternary propargylic center, fixing in
two methylene carbons the tether connecting the
Table 1. PtCl2-mediated cycloisomerization reaction of compounds 1–6
Entry
Precursor
Time (h)
Isolated yields (%)
a
b
c
d
e
f
16a XZCOCH3
2 XZCOCCl3
3 XZCOC6H5
4 XZCO[3,4,5-(OCH3)3C6H2]
5 XZCO[4-(NO2)C6H4]
6 XZCO2C2H5
72
46
76a,7 (8)
85a (54)
9 (20)
11 (40)
12 (39)a,b
13 (34)
15 (11)
26a
62a
46a
22a
10 (11)
14(3)
a For 3: Plus 4.5 h at 60 8C. For 4: Plus 23 h at 60 8C. For 5: At 60 8C. For 6: Plus 19 h at 60 8C.
b 80% pure (glc).

S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
4795
and, by comparison with the substrates having gem-
dimethyl groups at the allylic position (Scheme 1),4a the
presence of two methyl groups at the terminal double bond
retards the speed of the reaction, giving moderate to low
yields of the cycloisomerization reaction products. This is
possibly a consequence of the higher steric hinderance at the
transition state, due to the presence of the methyl groups at
the terminal position, and points out to an accelerating
factor due to the Thorpe-Ingold effect of the gem-dimethyl
groups in the precursors shown in Scheme 1.4a Regarding
the different tested acyl groups and their different
anchimeric assistance properties, it seems that groups
having functional moieties directly bonded to the carbonyl
group, with a strong -I effect, as the trichloromethyl or the
ethoxy in the carbonate, do not favour the Rautenstrauch
isomerization, while electron-donating groups as the methyl
or the phenyl accelerate it.
Scheme 4. Conditions: From 8 (XZCOCH3): 15 min, rt (cis/trans: 1/3;
66%). From 11 (XZCOC6H5): 24 h, rt (only trans; 50%).
the O-trichloroacetyl group due to the electron-withdrawing
chlorine atoms.
With this result in mind we tested new substrates containing
differently substitued benzoyl groups (3–5). From com-
pound 3, after PtCl2 catalyzed rearrangement, the allenyl
ester 10 (11%) and product 11 (40%) (Table 1, entry c) were
isolated, confirming the suitability of the unsubstituted
benzoyl group to participate in this cycloisomerization
reaction. In order to explore the influence of donor or
electron-withdrawing substituents at the aromatic moiety
we submitted to cyclization precursors 4 and 5, with three
methoxy and with one nitro groups, respectively, at the
aromatic ring. As we can see, precursors 4 and 5 gave
products 12 (39% yield) (Table 1, entry d) and 13 (34%
yield) (Table 1, entry e) in moderate yield, and no traces of
the allenyl derived molecules were detected. All these new
compounds gave excellent analytical and spectroscopic
data, similar to those described for the parent derivative 8.
In overall, and in good agreement with what has been
reported,8a even an electron-withdrawing group, as the
4-nitrobenzoyl, promotes the cycloisomerization reaction,
but less efficiently than the benzoyl or the substituted
trimethoxybenzoyl group; in addition, the benzoyl behaves
less efficiently than the acetyl group, probably due to a steric
effect.
The formation of compounds 8, 9, 11–13 and 15 constitutes
a simple, but efficient entry into the skeleton of the ‘carane’
family of natural products.9 As expected, after treatment
with K2CO3, MeOH, acetate 8 afforded a mixture of cis and
trans-caran-2-one (16) in a 1/3 ratio (Scheme 4), that we
1
were unable to separate by chromatography. The H NMR
analysis and the comparison of these data with those
reported for these compounds9a clearly showed that our
major compound was the trans isomer. The formation of
major trans-isomer 16 is in good agreement with the
reported base isomerization of mixtures of cis and trans-
caran-2-one leading to the major, thermodynamically more
stable trans isomer.9b Similarly, compound 11, after a long
base-mediated methanolysis, gave only trans-isomer 16
(Scheme 4).
Next we submitted to cycloisomerization the known
precursors 1710 (Scheme 5) and 1810 (Scheme 6) in order
to test the influence of a proximal triple substituted alkene,
the stereochemistry at this double bond, as well as the
presence of a second, terminal trisubstituted double bond.
Compounds 17 (Scheme 5) and 18 (Scheme 6) have been
synthesized using the same synthetic sequence, as pre-
viously shown for compounds 1–6 (Schemes 2 and 3),
starting from commercial neryl and geranyl acetones,
respectively.
In this context, the analysis of the reactivity of a carbonate
group seemed to us very promising. Thus, we prepared
precursor 6 (Scheme 3). Unfortunately, this compound gave
a complex reaction mixture, and we only could isolate
products 14 and 15 in poor yield (Table 1, entry f).
From these results we conclude that the acetyl group is the
best migrating group in terms of simplicity and efficiency
Scheme 5. Reagents: (a) Ethynylmagnesium bromide, THF/Et2O (1:1), rt, 4 h (80%); (b) Ac2O, py, DMAP, rt, 40 h (63%); (c) PtCl2 (5%), toluene, 40 8C, 32 h.

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S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
Scheme 6. Reagents: (a) Ethynylmagnesium bromide, THF/Et2O (1:1), rt, 4 h (70%); (b) Ac2O, py, DMAP, rt, 24 h (63%); (c) PtCl2 (5%), toluene, 80 8C, 32 h.
Acetate 1710 gave the known allene 1911 and compound 20
(Scheme 5). After selective NOE experiments in the H
NMR spectrum we could determine that in acetate 20 the
methyl at C-7 was cis to the cyclopropyl protons at C-1 and
C-6.
product 24 (Scheme 7) in a quick reaction and in
quantitative chemical yield (99%). The clean and high
yielding reaction of precursor 23, compared with the results
obtained in the previously reported results4a (Scheme 1) or
the results obtained from precursors 1–6 (Table 1) clearly
show the importance of steric interactions in the transition
state in transition-metal catalyzed reactions.12
1
Starting from precursor 18,10 after PtCl2-mediated cyclo-
isomerization, we isolated the known allene 2111 and
compound 22 (Scheme 6), in lower yields compared with
the results obtained form its isomer 17. The relative
configuration in compound 22, around the fused rings,
was proved to be as shown in Scheme 6, as no NOE effect
was observed between the methyl group at C-7 and the
cyclopropyl protons at C-1 and C-6 in the 1H NMR
spectrum.
Next, product 24 was submitted to the basic methanolysis to
give the known ketone 2513 (Scheme 7), isolated as a
mixture of isomers cis/trans in 1.5:1 ratio, in 61% yield. The
spectroscopic data of this mixture were in good agreement
with the reported values for these compounds.13a
Finally, note that as an added bonus of the present
cycloisomerization reaction of readily available propargylic
carboxylates, the synthesis of a,b-unsaturated cyclopropyl
ketones 16 and 25, in a two-step protocol (PtCl2-mediated
cycloisomerization plus basic methanolysis), constitutes an
alternative to the usual unfriendly, intramolecular cyclo-
propanation of unsaturated a-diazocarbonyl derivatives,
prepared by reaction of carboxylic acid chlorides and
diazomethane.14
From these results we conclude that the PtCl2 -promoted
cycloisomerization process of trisubstitued alkenes is
possible, proceeds stereospecifically giving cis- or trans-
products, depending on the stereochemistry at the double
bond on the precursor, the Z isomer affording the cis isomer,
while the E isomer leads to the corresponding trans
derivative. Finally, note that the terminal double bond was
not involved in the cyclization reaction. These results show
also that the efficiency of the reaction is critically dependent
on the stereochemistry at the central double bond: the
Z-isomer provided a moderate yield of the bicyclic
derivative, the E isomer giving a complex reaction mixture
and the final products in poor overall chemical yields.
Regarding the mechanism of this PtCl2-madiated cyclo-
isomerization reaction, in Scheme 8 we show a tentative
proposal based on previous findings.3g,4a,15 The intra-
molecular ester attack to the polarized metal-alkyne
complex should give intermediate D that evolves to Pt
carbene E, whose final reaction with the terminal double
bond results in the formation of compound 8.
Our next precursor was acetate 23 (Scheme 7), where we
have eliminated the methyl groups on the double bond or at
allylic positions. Compound 236b has been synthesized from
commercial 5-hexen-2-one following the standard
sequence. The isomerization of precursor 23 afforded
In summary, in this paper we have presented additional
synthetic details on the scope and generality of the PtCl2-
catalyzed cycloisomerization of unsaturated propargylic
Scheme 7. Reagents: (a) Ethynylmagnesium bromide, THF/Et2O (1:1), rt, 3 h (50%); then, Ac2O, py, DMAP, rt, 12 h (67%); (b) PtCl2 (5%), toluene, rt, 18 h
(99%); (c) K2CO3, MeOH, rt , 18 h (61%).

S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
4797
Scheme 8. Proposed mechanism for the PtCl2-mediated cycloisomerization of compound 1.
carboxylates.4,5 This reaction yields differently function-
alized bicyclo[4.1.0]heptane enol esters from moderate to
good yield, in a very diastereoselective and stereospecific
manner. Basic metanolysis (K2CO3, MeOH) of these
intermediates gave mixtures of cis- and trans-caran-2-
ones. The formation of these bicyclo[4.1.0]heptane deriva-
tives is a simple but efficient entry into the skeleton of the
‘carane’ family of natural products.16
3.4. General procedure for methanolysis of enol esters
Solid potassium carbonate (2.0 equiv) was added to a
solution of the respective enol ester in methanol (0.05 M).
The reaction mixture, stirred at rt until complete reaction,
was quenched by adding brine. The reaction mixture was
extracted by diethyl ether and dried over anhydrous
Na2SO4. Purification by flash column chromatography
(EtOAc/hexane) afforded the corresponding ketones.
3. Experimental
3.1. General methods
3.4.1. 3,7-Dimethyl-oct-6-en-1-yn-3-yl acetate (‘dehydro-
dehydrolinalyl acetate’) (1).6a A solution of 6-methyl-5-
heptene-2-one (0.86 g, 6.8 mmol) in a mixture of dry THF/
diethyl ether (1:1) (4 mL) was added dropwise, at rt, to a
solution of ethynylmagnesium bromide (16 mL, 8.16 mmol,
0.5 M in THF) in anhydrous diethyl ether (16 mL), under
argon. The reaction mixture was stirred at rt for 3 h. Then,
water (25 mL) was added to quench the reaction and the
mixture was extracted with diethyl ether (25!3 mL). The
combined organic layers were washed with brine and dried
over anhydrous Na2SO4. The solvent was evaporated under
vacuum. Purification by flash chromatography (EtOAc/
hexane, 5:95) gave 3,7-dimethyl-oct-6-en-1-yn-3-ol
(‘dehydrolinalool’) (0.75 g, 72% yield) [1H NMR
(200 MHz, CDCl3) d 5.18 (tm, JZ7.4 Hz, 1H, H-6), 2.47
(s, 1H, H-1), 2.30–2.17 (m, 2H, H-5), 2.20 (br s, 1H, OH),
1.72 (s, 3H, H-8)*, 1.71 (s, 3H, H-9)*, 1.72–1.56 (m, 2H,
H-4), 1.51 (s, 3H, H-10)]. Following the general procedure
Melting points were determined on a digital melting-point
apparatus (Electrothermal) and are uncorrected. H NMR
1
and 13C NMR spectra were recorded in CDCl3, at 300.13
and at 75.47 MHz (Bruker Avance-300). TLC was
performed on Silica F254 (Merck) and detection by UV
light at 254 nm or by charring with phosphomolybdic-
H2SO4 reagent. Column chromatography was effected on
Silica Gel 60 (Merck, 230 mesh). The assignment of
chemical shifts are based on standard NMR experiments
1
(1H, 13C, DEPT, H–1H COSY, HMQC, HMBC). In the
NMR spectra values with (*) can be interchanged.
3.2. General procedure for the PtCl2-catalyzed
cycloisomerization reaction
for the esterification reaction, to
a solution of
To a degassed solution of the precursor in dry toluene
(0.025 M) PtCl2 (0.05 equiv) was added at room tempera-
ture (rt), under argon. The reaction mixture was stirred at
40–80 8C until complete reaction. Then, the reaction
mixture was filtered and the solvent was evaporated under
vacuum. Purification by flash chromatography, eluting with
mixtures of EtOAc/hexane gave the corresponding
products.
‘dehydrolinalool’ (337 mg, 2.21 mmol) in dry pyridine
(4 mL), DMAP (120 mg, 0.98 mmol) and acetic anhydride
(339.2 mg, 5 mL, 3.32 mmol) were added. The reaction
mixture was stirred 12 h at rt. The solvent was evaporated
under vacuum and the crude was purified by flash
chromatography (EtOAc/hexane, 2:98) to furnish (1)
(350 mg, 81% yield) as a colorless oil, that showed
spectroscopic data [1H NMR (200 MHz, CDCl3) d 5.08
(tm, JZ7.0 Hz, 1H, H-6), 2.53 (s, 1H, H-1), 2.15–2.08 (m,
2H, H-5), 1.99 (s, 3H, OCOCH3), 1.95–1.69 (m, 2H, H-4),
1.65 (s, 6H, H-8*, H-10), 1.31 (s, 3H, H-9*)] in agreement
with the structure of this known product.6a
3.3. General procedure for the esterification reaction
To a solution of the respective alcohol in dry pyridine,
DMAP (0.2 equiv) and the required acid chloride (or acid
anhydride) (1.5 equiv) were added. The reaction mixture
was refluxed until complete reaction. Then, the solvent was
evaporated under vacuum, the crude was dissolved in
dichloromethane and washed with an aqueous saturated
solution of NaHCO3, brine and water. Purification by flash
chromatography eluting with mixtures of EtOAc/hexane
gave the corresponding products.
3.4.2. 3,7-Dimethyl-octa-1,2,6-trien-1-yl acetate (7)6a,7
and 3,7,7-trimethyl-bicyclo[4.1.0.]hept-2-en-2-yl acetate
(‘2-acetoxy-2-carene’) (8).5a Following the general pro-
cedure for the PtCl2-catalyzed cycloisomerisation reaction,
to a degassed solution of compound (1) (130.7 mg,
0.55 mmol) in dry toluene (27 mL) PtCl2 (7.32 mg,
0.027 mmol) was added. The reaction mixture was stirred

4798
S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
for 72 h at 40 8C. Purification by flash chromatography
(EtOAc/hexane, 0.5:99.5) afforded (7)6a,7 (10.3 mg, 8%
yield) and 2-acetoxy-2-caren (8)5a (70.7 mg, 54% yield).
Both compounds (76a,7 and 85a) and are known and showed
analytical and spectroscopic data, in good agreement with
those described in literature. 7: Oil; IR (film) n 3065, 2919,
1230, 1218, 1077 cmK1 1H NMR (75 MHz, CDCl3) d
;
2.38–2.20 (m, 1H, H-4), 1.98–1.80 (m, 2H, H-40, H-5),
1.78–1.68 (m, 1H, H-50;), 1.66 (s, 3H, H-10), 1.28–1.10 (m,
2H, H-1, H-6), 1.10 (s, 3H, H-9)*, 1.05 (s, 3H, H-8)*; 13C
NMR (300 MHz, CDCl3) d 160.4 (OCOCCl3), 142.7 (C-2),
121.2 (C-3), 90.5 (OCOCCl3), 30.3 (C-4), 28.2 (C-8)*, 25.9
(C-7), 25.4 (C-6)**, 23.2 (C-1)**, 18.0 (C-5), 16.1 (2C,
C-10, C-9*); MS (70 eV) m/z 296, 298 (MC, 6, 6), 281, 283
(MCK15, 4, 4), 189, 191 (8, 8), 151 (9), 135 (18), 123 (21),
119 (100), 117 (34), 91 (38), 81 (31), 69 (24). Anal. Calcd
for C12H15Cl3O2: C, 48.43; H, 5.08. Found: C, 48.66; H,
5.28.
2857, 1976, 1750 (OCOCH3), 1445, 1368, 1216, 1148 cmK1
;
1H NMR (300 MHz, CDCl3) d 7.28 (s, 1H, H-1), 5.12 (tm,
JZ7.1 Hz, 1H, H-6), 2.15 (m, 2H, H-5), 2.13 (s, 3H,
OCOCH3), 2.10–2.01 (m, 2H, H-4), 1.78 (d, JZ2.0 Hz, 3H,
H-10), 1.62 (s, 3H, H-8)*, 1.59 (s, 3H, H-9)*; 13C NMR
(75 MHz, CDCl3) d 189.7 (C-2), 169.2 (OCOCH3), 132.5
(C-7), 123.6 (C-6), 116.2 (C-3), 110.1 (C-1), 35.6 (C-4),
26.3 (C-5), 26.0 (C-9), 21.3 (OCOCH3), 20.9 (C-10), 18.1
(C-8); MS (70 eV) m/z 195 (MCC1, 4), 151 (30), 134 (21),
123 (30), 109 (42), 84 (71), 69 (43), 49 711), 43 (100). Anal.
Calcd for C12H18O2: C, 74.19; H, 9.34. Found: C, 74.30; H,
9.18. 8: Oil; IR (film) n 2926, 2864, 1756 (OCOCH3), 1698,
1450, 1368, 1213, 1165 cmK1; 1H NMR (300 MHz, CDCl3)
d 2.33–2.20 (m, 1H, H-4), 2.16 (s, 3H, OCOCH3), 1.85–1.75
(m, 01H, H-5), 1.75–1.65 (m, 1H, H-40), 1.65–1.59 (m, 1H,
H-5 ), 1.55 (s, 3H, H-10), 1.12–1.06 (m, 2H, H-1, H-6), 1.07
(s, 3H, H-9)*, 1.00 (s, 3H, H-8)*; 13C NMR (75 MHz,
CDCl3) d 169.8 (OCOCH3), 141.7 (C-2), 119.4 (C-3), 29.9
(C-4), 28.3 (C-8)*, 25.2 (C-7), 24.9 (C-6)**, 24.1 (C-1)**,
21.3 (OCOCH3), 17.9 (C-5), 16.4 (C-10), 16.1 (C-9)*; MS
(70 eV) m/z 194 (MC, 4), 193 (MCK1, 4), 166 (6), 152
(49), 137 (38), 123 (22), 109 (100), 91 (27), 83 (13), 77 (16),
69 (29), 55 (17), 43 (83). Anal. Calcd for C12H18O2: C,
74.19; H, 9.34. Found: C, 73.96; H, 9.60.
3.4.5. 3,7-Dimethyloct-6-en-1-yn-3-yl benzoate (3).
Following the general procedure for the esterification
reaction, to a solution of ‘dehydrolinalool’ (250.1 mg,
1.65 mmol) in dry pyridine (5 mL), DMAP (40.2 mg,
0.33 mmol) and benzoyl chloride (0.46 mL, 3.29 mmol)
were added. The reaction mixture was refluxed for 46 h.
After standard work-up, flash chromatography (EtOAc/
hexane, 2:98) gave (3) (272.0 mg, 64% yield) as a colorless
thick oil: IR (film) n 3301, 3062, 2971, 2926, 2117, 1725
(OCOPh), 1601, 1585, 1491, 1451, 1375, 1314, 1279,
1
1168 cmK1; H NMR (300 MHz, CDCl3) d 8.05 (m, 2H),
7.55 (m, 1H), 7.49 (m, 2H) (5H, OCOC6H5), 5.16 (tm, JZ
7.4 Hz, 1H, H-6), 2.61 (s, 1H, H-1), 2.35–2.22 (m, 2H, H-5),
2.15–2.06 (ddd, JZ6.1 Hz, JZ10.7 Hz, JZ13.4 Hz, 1H,
H-4), 2.01–1.92 (ddd, JZ5.4 Hz, JZ10.7 Hz, JZ13.4 Hz
1H, H-40), 1.82 (s, 3H, H-10), 1.68 (s, 3H, H-8)*, 1.63 (s,
3H, H-9)*; 13C NMR (75 MHz, CDCl3) d 164.7
(OCOC6H5), 132.8 (C-7), 132.9, 132.3, 130.8, 128.3
(COC6H5), 123.1 (C-6), 83.6 (C-2), 75.2 (C-3), 73.5
(C-1), 41.6 (C-4), 26.5 (C-10), 25.6 (C-9), 22.9 (C-5),
17.6 (C-8); MS (70 eV) m/z 256 (MC, 12), 134 (25), 119
(78), 105 (100), 91 (38), 77 (61), 69 (29), 51 (21), 41 (28).
Anal. Calcd for C17H20O2: C, 79.65; H, 7.86. Found: C,
79.36; H, 8.14.
3.4.3. 3,7-Dimethyloct-6-en-1-yn-3-yl trichloroacetate
(2). Following the general procedure for the esterification
reaction, to a solution of ‘dehydrolinalool’ (115.8 mg,
0.76 mmol) in dry pyridine (3 mL) DMAP (18.6 mg,
0.15 mmol) and trichloroacetic anhydride (0.35 mL,
1.14 mmol) were added. The reaction mixture was stirred
at rt for 45 min. After usual workup, flash chromatography
(EtOAc/hexane, 0.5:99.5) gave compound 2 (178.5 mg,
79% yield) as a colorless oil: IR (film) n 3305, 2971, 2927,
2123, 1771 (OCO), 1673, 1449, 1377, 1343, 1238,
3.4.6. 3,7-Dimethyl-octa-1,2,6-trien-1-yl benzoate (10)
and 3,7,7-trimethyl-bicyclo[4.1.0.]hept-2-en-2-yl benzo-
ate (11). Following the general procedure for the PtCl2-
catalyzed cycloisomerisation reaction, to a degassed
solution of compound (3) (130.7 mg, 0.55 mmol) in dry
toluene (20 mL), PtCl2 (6.79 mg, 0.027 mmol) was added.
The reaction mixture was stirred for 26 h at 40 8C and for
4.5 h at 60 8C. Purification by flash chromatography
(EtOAc/hexane, 0.5:99.5) afforded compounds 10
(14.4 mg, 11% yield) and 11 (52.3 mg, 40% yield). 10:
Oil; IR (film) n 3065, 2919, 2857, 1976, 1750 (OCOPh),
1445, 1368, 1216, 1148 cmK1; 1H NMR (300 MHz, CDCl3)
d 8.12–7.99 (m, 2H), 7.59–7.46 (m, 1H), 7.40–7.35 (m, 2H)
(5H, OCOC6H5), 7.59–7.46 (m, 1H, H-1), 5.15 (tm, JZ
7.2 Hz, 1H, H-6), 2.18–1.98 (m, 4H, H-4, H-5), 1.80 (d, JZ
1.8 Hz, 3H, H-10), 1.64 (s, 3H, H-8)*, 1.58 (s, 3H, H-9)*;
13C NMR (75 MHz, CDCl3) d 190.4 (C-2), 165.1
(OCOC6H5), 133.6, 132.5, 130.2, 128.8 (OCOC6H5),
130.0 (C-7), 123.9 (C-6), 116.3 (C-3), 110.4 (C-1), 35.7
(C-4), 26.3 (C-5), 26.0 (C-9), 21.0 (C-10), 18.2 (C-8); MS
(70 eV) m/z 256 (MC, 1), 187 (7), 151 (11), 119 (5), 105
(100), 77 (38), 51 (10), 41 (15). Anal. Calcd for C17H20O2:
C, 79.65; H, 7.86. Found: C, 79.72; H, 8.01. 11: Oil; IR
(film) n 3066, 2922, 1729 (OCOPh), 1601, 1584, 1492,
1451, 1375, 1314, 1272, 1176, 1106, 1069, 1026 cmK1; 1H
1
1165 cmK1; H NMR (300 MHz, CDCl3) d 5.16 (tm, JZ
7.0 Hz, 1H, H-6), 2.71 (s, 1H, H-1), 2.38–2.13 (m, 2H, H-5),
2.08–1.82 (m, 2H, H-4), 1.82 (s, 3H, H-10), 1.71 (s, 3H,
H-8)*, 1.65 (s, 3H, H-9)*; 13C NMR (75 MHz, CDCl3) d
159.4 (OCOCCl3), 132.8 (C-7), 122.4 (C-6), 91.5
(OCOCCl3), 81.2 (C-2), 80.3 (C-3), 75.4 (C-1), 41.2
(C-4), 25.7 (C-10), 25.6 (C-9), 22.7 (C-5), 17.5 (C-8); MS
(70 eV) m/z 134, 135 (5, 5), 119 (88), 105 (21), 91 (40), 84
(36), 77 (15), 69 (100), 55 (19), 49 (44), 41 (63). Anal. Calcd
for C12H15Cl3O2: C, 48.43; H, 5.08. Found: C, 48.36; H,
4.75.
3.4.4. 3,7,7-Trimethyl-bicyclo[4.1.0.]hept-2-en-2-yl tri-
chloroacetate (9). Following the general procedure for
the PtCl2-catalyzed cycloisomerisation reaction, to a
degassed solution of 3,7-dimethyl-1-octyn-6-en-3-trichloro-
acetate (2) (105.7 mg, 0.37 mmol) in dry toluene (15 mL),
PtCl2 (4.98 mg, 0.18 mmol) was added. The reaction
mixture was stirred for 46 h at 40 8C until complete the
reaction. After flash chromatography (EtOAc/hexane, 1:99)
(9) (14.7 mg, 20% yield) was isolated as a colorless oil: IR
(film) n 2923, 2865, 1774 (OCO), 1702, 1450, 1376, 1354,

S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
4799
NMR (300 MHz, CDCl3) d 8.14 (m, 2H), 7.58 (m, 1H), 7.49
(m, 2H) (5H, OCOC6H5), 2.35–2.00 (m, 1H, H-4), 1.87–
1.65 (m, 2H, H-5, H-40), 1.60–1.55 (m, 1H, H-50), 1.62 (s,
3H, H-10), 1.40–1.15 (m, 2H, H-1, H-6), 1.11 (s, 3H, H-9)*,
1.09 (s, 3H, H-8)*; 13C NMR (75 MHz, CDCl3) d 165.3
(OCOC6H5), 142.0 (C-2), 135.1, 130.3, 129.9, 128.7
(OCOC6H5), 119.6 (C-3), 30.1 (C-4), 28.4 (C-8)*, 25.3
(C-7), 25.1 (C-6)**, 24.3 (C-1)**, 18.1 (C-5), 16.5 (C-10),
16.2 (C-9)*; MS (70 eV) m/z 256 (MC, 38), 151 (3), 134 (7),
105 (100), 77 (56), 41 (12). Anal. Calcd for C17H20O2: C,
79.65; H, 7.86. Found: C, 79.54; H, 7.69.
reaction, to a solution of ‘dehydrolinalool’ (500.0 mg,
3.29 mmol) in dry pyridine (5 mL), DMAP (80.28 mg,
0.65 mmol) and 4-nitrobenzoyl chloride (915.3 mg,
4.93 mmol) were added. The reaction mixture was heated
at 80 8C for 16 h until complete reaction. Purification by
flash column chromatography (EtOAc/hexane, 4:96)
afforded (5) (660.0 mg, 70% yield) as white crystals: mp
73–74 8C; IR (KBr) n 3298, 3119, 2971, 2921, 1726
(OCOAr), 1607, 1590, 1526, 1446, 1377, 1351, 1323,
1290, 1166 cmK1; 1H NMR (300 MHz, CDCl3) d 8.30 (dm,
JZ9.0 Hz, 2H, OCOC6H4NO2), 8.19 (d, JZ9.0 Hz, 2H,
OCOC6H4NO2), 5.19 (tm, JZ7.1 Hz, 1H, H-6), 2.69 (s, 1H,
H-1), 2.40–2.20 (m, 2H, H-5), 2.18–1.76 (m, 2H, H-4), 1.87
(s, 3H, H-10), 1.71 (s, 3H, H-8)*, 1.66 (s, 3H, H-9)*; 13C
NMR (75 MHz, CDCl3) d 165.4 (OCOC6H4NO2), 153.0,
138.8, 135.1, 126.0 (OCOC6H4NO2), 133.2 (C-7), 125.4
(C-6), 85.5 (C-2), 79.0 (C-3), 76.8 (C-1), 43.9 (C-4), 28.9
(C-10), 28.1 (C-9), 25.5 (C-5), 20.1 (C-8); MS (70 eV) m/z
301 (MC, 1), 150 (70), 134 (8), 119 (100), 104 (29), 91 (42),
79 (9), 76 (21), 41 (37). Anal. Calcd for C17H19NO4: C,
67.76; H, 6.36; N, 4.65. Found: C, 67.42; H, 6.59; N, 4.77.
3.4.7.
3,7-Dimethyloct-6-en-1-yn-3-yl(30,40,50)-tri-
methoxy benzoate (4). Following the general procedure
for the esterification reaction a solution of ‘dehydrolinalool’
(290.0 mg, 1.92 mmol) in dry pyridine (5 mL), DMAP
(46.8 mg, 0.38 mmol) and 3,4,5-trimethoxybenzoyl
chloride (886 mg, 3.84 mmol) were added. The reaction
mixture was refluxed for 24 h. After usual workup,
purification by flash chromatography (EtOAc/hexane,
4:96) furnished product 4 (272.0 mg, 49% yield) as white
crystals: mp 45–47 8C; IR (film) n 3234, 2973, 2936, 2111,
1721 (OCOAr), 1687, 1590, 1504, 1455, 1413, 1372, 1335,
3.4.10. 3,7,7-Trimethyl-bicyclo[4.1.0.]hept-2-en-2-yl
4-nitrobenzoate (13). Following the general procedure for
the PtCl2-catalyzed cycloisomerisation reaction, to a
degassed solution of compound (5) (303.9 mg, 1.06 mmol)
in dry toluene (43 mL), PtCl2 (14.08 mg, 0.053 mmol) was
added. The reaction mixture was stirred for 46 h at 60 8C.
Purification by flash chromatography (EtOAc/hexane, 4:96)
gave compound 13 (103.3 mg, 34% yield) as yellow
crystals: mp 78–80 8C; IR (KBr) n 2918, 1724 (OCOAr),
1605, 1529, 1449, 1349, 1320, 1276, 1166 cmK1; 1H NMR
(300 MHz, CDCl3) d 8.32 (s, 4H, OCOC6H4NO2), 2.41–
2.24 (m, 1H,0H-4), 2.00–1.80 (m, 2H, H-5, H-40), 1.78–1.69
(m, 1H, H-5 ), 1.61 (s, 3H, H-10), 1.24–1.18 (m, 2H, H-1,
H-6), 1.09 (s, 2!3H, 6H, H-8, H-9); 13C NMR (75 MHz,
CDCl3) d 166.1 (OCOC6H4NO2), 153.7, 144.7, 134.2, 126.7
(OCOC6H4NO2), 142.4 (C-2), 117.2 (C-3), 32.9 (C-4), 28.3
(C-8)*, 28.3 (C-7), 27.9 (C-6)**, 26.9 (C-1)**, 20.7 (C-5),
19.3 (C-10), 18.9 (C-9)*; MS (70 eV) m/z 301 (MC, 55),
286 (6), 258 (5), 231 (4), 150 (100), 134 (12), 119 (17), 104
(34), 92 (15), 81 (7), 76 (16). Anal. Calcd for C17H19NO4:
C, 67.76; H, 6.36; N, 4.65. Found: C, 67.52; H, 6.60; N,
4.98.
1
1247, 1222, 1162 cmK1; H NMR (300 MHz, CDCl3) d
7.28 [s, 2H, OCOC6H2(OCH3)3], 5.18 (tm, JZ7.0 Hz, 1H,
H-6), 3.90 (s, 9H, 3!CH3O), 2.62 (s, 1H, H-1), 2.40–2.21
(m, 2H, H-5), 2.20–1.95 (m, 2H, H-4), 1.82 (s, 3H, H-10),
1.65 (s, 3H, H-8)*, 1.61 (s, 3H, H-9)*; 13C NMR (75 MHz,
CDCl3) d 165.5 (OCOAr), 152.9, 132.5, 125.9, 106.9
[OCOC6H2(OCH3)3], 132.1 (C-7), 123.2 (C-6), 83.7 (C-2),
75.5 (C-3), 73.7 (C-1), 61.0 (OCH3), 56.2 (2!CH3O), 41.9
(C-4), 26.6 (C-10), 25.7 (C-9), 23.1 (C-5), 17.6 (C-8); MS
(70 eV) m/z 346 (MC, 2), 212 (46), 195 (100), 134 (16), 119
(78), 91 (17), 41 (20). Anal. Calcd for C20H26O5: C, 69.34;
H, 7.56. Found: C, 69.15; H, 7.48.
3.4.8. 3,7,7-Trimethyl-bicyclo[4.1.0.]hept-2-en-2-yl
30,40,50-trimethoxybenzoate (12). Following the general
procedure for the PtCl2-catalyzed cycloisomerisation
reaction, to a degassed solution of compound 4 (101.6 mg,
0.29 mmol) in dry toluene (12 mL), PtCl2 (3.9 mg,
0.14 mmol) was added. The reaction mixture was stirred
for 62 h at 40 8C and for 23 h at 60 8C. Flash chromato-
graphy (EtOAc/hexane, 4:96) gave compound 12 [39.3 mg,
39% yield, (80% purity by glc)], as a light yellow oil: IR
(film) n 2925, 2853, 1727 (OCO), 1591, 1504, 1463, 1416,
3.4.11. Carbonic acid (3,7-dimethyl-1-octyn-6-en-3-yl)
ethyl ester (6). A solution of of 6-methyl-5-heptene-2-one
(1.0 g, 7.94 mmol) in a mixture of THF/diethyl ether (1:1)
(20 mL) was added dropwise, at rt, to a solution of
ethynylmagnesium bromide (20 mL, 9.53 mmol, 0.5 M in
THF), under argon. The reaction mixture was stirred at rt for
2 h. After completion of reaction, ethyl chloroformiate
(1.12 g, 10.32 mmol) was added at 0 8C and the reaction was
stirred at rt for 5 h. Then reaction was quenched by adding
cold water (100 mL), and the organic layer was extracted
with diethyl ether (100!3 mL). The combined organic
layers were washed with brine and dried over anhydrous
Na2SO4. After evaporation of the solvent, purification by
flash chromatography (EtOAc/hexane, 0.5:99.5) gave (6)
(1.22 g, 68% yield) as a yellow oil: IR (film) n 3290, 2981,
2930, 2120, 1754 [OC(O)OEt], 1447, 1371, 1261,
1
1337, 1106 cmK1; H NMR (300 MHz, CDCl3) d 7.40 [s,
2H, OCOC6H2(OCH3)3], 3.95 (s, 6H, 2!CH3O), 3.94 (s,
3H, CH3O), 2.40–2.18 (m, 1H, H-4), 2.00–180 (m, 2H, H-5,
H-40), 1.79–1.66 (m, 1H, H-50), 1.61 (s, 3H, H-10), 1.25–
1.18 (m, 2H, H-1, H-6), 1.10 (s, 3H, H-8)*, 1.09 (s, 3H,
H-9)*; 13C NMR (75 MHz, CDCl3) d 164.9 [OCOC6H2-
(OCH3)3], 153.3, 135.0, 125.6, 107.5 [OCOC6H2(OCH3)3],
142.0 (C-2), 119.3 (C-3), 61.3 (CH3O), 56.6 (2!CH3O),
30.0 (C-4), 28.4 (C-8)*, 26.0 (C-7), 25.4 (C-6)**, 24.5
(C-1)**, 17.9 (C-5), 16.5 (C-10), 16.2 (C-9)*; MS (70 eV)
m/z 346 (MC, 1), 229 (8), 212 (11), 209 (4), 195 (100), 167
(5), 152 (8), 137 (8), 123 (5), 111 (5), 95 (8), 85 (15), 77
(12), 69 (16), 51 (7), 43 (19). Anal. Calcd for C20H26O5: C,
69.34; H, 7.56. Found: C, 69.30; H, 7.95.
1
3.4.9. 3,7-Dimethyloct-6-en-1-yn-3-yl 4-nitrobenzoate
(5). Following the general procedure for the esterification
1167 cmK1; H NMR (300 MHz, CDCl3) d 5.08 (m, 1H,
H-6), 4.15 (q, JZ7.0 Hz, 2H, OCO2CH2CH3), 2.58 (s, 1H,

4800
S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
H-1), 2.25–2.08 (m, 2H, H-5), 2.05–1.90 (m, 1H, H-4),
1.90–1.75 (m, 1H, H-50), 1.69 (s, 3H, H-10), 1.66 (s, 3H,
H-8)*, 1.60 (s, 3H, H-9)*, 1.27 (t, JZ7.0 Hz, 3H, OCO2-
CH2CH3); 13C NMR (75 MHz, CDCl3) d 153.3 (OCO2-
CH2CH3), 132.8 (C-7), 123.3 (C-6), 83.6 (C-2), 77.5 (C-3),
74.2 (C-1), 63.9 (OCO2CH2CH3), 41.5 (C-4), 26.6 (C-10),
26.0 (C-9), 23.2 (C-5), 18.0 (C-8), 14.6 (OCO2CH2CH3);
MS (70 eV) m/z 165 (4), 152 (10), 137 (23), 119 (100), 109
(19), 105 (16), 91 (49), 81 (8), 79 (12), 69 (58), 55 (13), 49
(55), 41 (35). Anal. Calcd for C13H20O3: C, 69.61; H, 8.99.
Found: C, 69.50; H, 9.02.
identical spectroscopic data to those described for these
isomers in literature9a: Oil; IR (film) n 2931, 2869, 1682,
1454, 1376, 1225, 1179 cmK1; 1H NMR (300 MHz, CDCl3)
d (major trans isomer) 1.99 (m, 1H, H-3), 1.82 (m, 2H, H-4),
1.57 (m, 2H, H-5), 1.44 (m, 1H, H-1), 1.22 (s, 3H, H-8), 1.17
(m, 1H, H-6), 1.16 (s, 3H, H-9), 1.06 (d, JZ6.6 Hz, 3H,
H-10); (minor cis isomer)9d 1.13 (s, 3H, H-8), 1.12 (s, 3H,
H-9), 1.04 (d, JZ6.6 Hz, 3H, H-10); 13C NMR (300 MHz,
CDCl3) d (major trans isomer) 212.2 (C-2), 43.7 (C-3), 35.9
(C-4), 35.7 (C-1), 32.4 (C-9), 29.8 (C-6), 28.2 (C-7), 19.3
(C-5), 17.0 (C-8), 15.9 (C-10); (minor isomer cis)9d 211.8
(C-2), 43.1 (C-3), 34.6 (C-1), 30.3 (C-9), 28.8 (C-4), 26.1
(C-6), 24.1 (C-7), 19.7 (C-5), 18.2 (C-8), 14.6 (C-10); MS
(70 eV) m/z 152 (MC, 2) 149 (77), 135 (40), 111 (37), 97
(55), 84 (95), 69 (92), 57 (100), 49 (75), 43 (75). Anal. Calcd
for C10H16O: C, 78.90; H, 10.59. Found: C, 78.65; H, 10.32.
3.4.12. Carbonic acid-(3,7-dimethyl-octa-1,2,6-trien-1-
yl) ethyl ester (14) and carbonic acid-(3,7,7-trimethyl-
bicyclo[4.1.0.]hept-2-en-2-yl) ethyl ester (15). Following
the general procedure for the PtCl2-catalyzed cyclo-
isomerization reaction, to a degassed solution of compound
6 (224 mg, 1.0 mmol) in dry toluene (25 mL), PtCl2
(13.3 mg, 0.05 mmol) was added. The reaction mixture
was stirred for 7 h at rt, heated at 40 8C for 22 h and at 60 8C
for 19 h. After usual workup, purification by flash
chromatography (EtOAc/hexane, 0.2:99.8) afforded com-
pounds 14 (9.9 mg, 3%) and 15 (25.2 mg, 11% yield, 80%
purity) as colorless oils. 14: IR (film) n 3068, 2927, 2855,
3.5. Methanolysis of enol ester 11
Following the general procedure for the methanolysis of
enol esters compound 11 (200 mg, 0.78 mmol), dissolved in
methanol (15 mL, 0.05 M), was treated with solid potassium
carbonate (153.1 mg, 1.56 mmol). The reaction mixture was
stirred at rt for 24 h. Purification by flash column
chromatography (EtOAc/hexane, 2:98) afforded trans-2-
caranone (16)9a (59.3 mg, 50% yield), which showed
identical spectroscopic to those observed for the major
isomer obtained in the methanolysis of compound 8.
1981, 1754, 1452, 1370, 1254, 1094 cmK1 1H NMR
;
(300 MHz, CDCl3) d 7.15 (br s, 1H, H-1), 5.32 (m, 1H,
H-6), 4.26 (q, JZ7.1 Hz, 2H, OCO2CH2CH3), 2.20–2.06
(m, 4H, H-4, H-5), 1.85 (d, JZ1.8 Hz, 3H, H-10), 1.70 (s,
3H, H-9)*, 1.62 (s, 3H, H-8)*, 1.28 (t, JZ7.1 Hz, 3H,
OCO2CH2CH3); 13C NMR (75 MHz, CDCl3) d 189.6 (C-2),
153.4 (OCO2CH2CH3), 132.6 (C-7), 123.9 (C-6), 117.4
(C-3), 112.3 (C-1), 64.9 (OCO2CH2CH3), 35.7 (C-4), 26.3
(C-5), 26.1 (C-9), 21.1 (C-10), 18.1 (C-8), 14.6 (OCO2-
CH2CH3); MS (70 eV) m/z 224 (MC, 2), 151 (25), 137 (18),
134 (38), 123 (37), 119 (50), 109 (62), 105 (78), 95 (31), 91
(47), 77 (37), 69 (84), 41 (100). Anal. Calcd for C13H20O3:
C, 69.61; H, 8.99. Found: C, 69.50; H, 9.02. 15: IR (film) n
2983, 2929, 2865, 1755 (OCO2CH2CH3), 1701, 1450, 1369,
3.5.1. (6Z)-3,7,11-Trimethyl-6,10-dodecadien-1-yn-3-yl
acetate (17).10 To a solution of neryl acetone (0.5 g,
2.6 mmol) in dry THF/diethyl ether (1:1) (2 mL) was added
dropwise ethynylmagnesium bromide (6.5 mL, 3.1 mmol,
0.5 M in THF), at rt, in anhydrous diethyl ether (5 mL),
under argon. The reaction mixture was stirred at rt for 4 h.
Then water (20 mL) was added to quench the reaction and
the mixture was extracted with diethyl ether (2!3 mL). The
combined organic layers were washed with brine and dried
over anhydrous Na2SO4. The solvent was evaporated under
vacuum. Purification by flash chromatography (EtOAc/
hexane, 2:98) gave (6Z)-3,7,11-trimethyl-1-dodeca-6,10-
dien-1-yn-3-ol (0.451 g, 80%) [1H NMR (200 MHz, CDCl3)
d 5.06–5.01 (m, 2H), 2.35 (s, 1H), 2.35–1.90 (m, 8H), 2.01
(br s, 1H), 1.59 (s, 6H), 1.51 (s, 3H), 1.39 (s, 3H)].
Following the General Protocol for the Esterification to a
solution of compound (6Z)-3,7,11-trimethyl-1-dodeca-6,10-
dien-1-yn-3-ol (0.2 g, 0.91 mmol) in dry pyridine (3 mL),
DMAP (21.96 mg, 0.18 mmol) and acetic anhydride
(139.2 mg, 0.19 mL, 1.37 mmol) were added. The reaction
mixture was stirred 40 h at rt. The solvent was evaporated
under vacuum and the crude was purified by flash
chromatography (EtOAc/hexane, 0.4:99.6) to give com-
pound 17 (150 mg, 63% yield) as a colorless oil, that
showed analytical and spectroscopic data [1H NMR
(200 MHz, CDCl3) d 5.02 (tm, JZ7.1 Hz, 2H), 2.46 (s,
1H), 2.20–2.00 (m, 2H), 1.98–1.94 (m, 4H), 1.93 (s, 3H),
1.90–1.65 (m, 4H), 1.58 (s, 9H), 1.51 (s, 3H)] in agreement
with the structure of this known product.10
1245, 1169, 1135, 1094, 1045, 1003 cmK1 1H NMR
;
(300 MHz, CDCl3) d 4.26 (q, JZ7.2 Hz, 2H, OCO2CH2-
CH3), 2.35–2.20 (m, 1H, H-4), 1.95–1.70 (m, 3H, H-5,
H-40), 1.61 (s, 3H, H-10), 1.37 (t, JZ7.2 Hz, 3H, OCO2-
CH2CH3), 1.30–1.12 (m, 2H, H-1, H-6), 1.09 (s, 3H, H-9)*,
1.01 (s, 3H, H-8)*; 13C NMR (75 MHz, CDCl3) d 153.8
(OCO2CH2CH3), 142.1 (C-2), 119.8 (C-3), 65.1 (OCO2-
CH2CH3), 30.2 (C-4), 28.2 (C-8)*, 25.4 (C-7), 25.0 (C-6)**,
23.8 (C-1)**, 17.9 (C-5), 16.1 (C-10), 16.0 (C-9)*, 14.6
(OCO2CH2CH3); MS (70 eV) m/z 224 (MC, 20), 165 (12),
152 (37), 137 (98), 123 (23), 119 (38), 109 (100), 105 (25),
91 (50), 81 (40), 69 (30), 51 (8), 41 (53). Anal. Calcd for
C13H20O3: C, 69.61; H, 8.99. Found: C, 69.70; H, 8.74.
3.4.13. Caran-2-one (16).9 Following the general procedure
for hydrolysis of enol esters, to a solution of ‘2-acetoxy-2-
carene’ (8) (70 mg, 0.36 mmol) in methanol (2 mL,
0.05 M), solid potassium carbonate (70.5 mg, 0.72 mmol)
was added. The reaction mixture was stirred at rt. After
complete reaction (15 min) the reaction was quenched by
adding brine (5 mL), extracted with diethyl ether and dried
over anhydrous Na2SO4. Purification by flash column
chromatography (EtOAc/hexane, 2:98) afforded caran-2-
one (16)9 (35.6 mg, 66% yield), isolated as an inseparable
mixture of cis/trans isomers in a 1:3 ratio, which showed
3.5.2. (6Z)-3,7,11-Trimethyl-1,2,6,10-dodecatetraen-1-yl
acetate (19) and (1S*,6R*,7R*)-3,7-dimethyl-7-(4-
methyl-3-pentenyl)bicyclo[4.1.0]hept-2-en-2-yl acetate
(20). Following the general procedure for the

S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
4801
PtCl2-catalyzed cycloisomerisation reaction, to a degassed
solution of compound 17 (100 mg, 0.382 mmol) in dry
toluene (15 mL) PtCl2 (5.1 mg, 0.19 mmol) was added. The
reaction mixture was stirred for 32 h at 40 8C. Purification
by flash chromatography (EtOAc/hexane, 0.4:99.6) afforded
compounds (19) {(13 mg, 10% yield, 80% pure)][1H NMR
(300 MHz, CDCl3) d 7.16 (s, 1H, H-1), 5.02 (m, 2H), 2.15–
1.90 (m, 8H), 2.03 (s, 3H), 1.73 [d, JZ2.0 Hz, 3H], 1.58 (s,
2!3H, 6H), 1.50 (s, 3H)] that showed spectroscopic data in
good agreement with those described in literature11} and
(20) (49 mg, 49% yield). 20: Oil; IR (film) n 2959, 2925,
The reaction mixture was stirred for 32 h at 80 8C.
Purification by flash chromatography (CH2Cl2/hexane,
1:9) afforded products 2111 (9.4 mg, 8% yield) and 22
(23.1 mg, 19% yield). 2111: Oil; 1H NMR (200 MHz,
CDCl3) d 7.27 (m, 1H, H-1), 5.12 (m, 2H, H-6, H-10), 2.13
(s, 3H, OCOCH3), 2.11–1.98 (m, 8H), 2.03 (s, 3H), 1.83 (d,
JZ1.8 Hz, 3H, H-15), 1.68 (s, 3H), 1.60 (s, 3H); 13C NMR
(75 MHz, CDCl3) d 189.8, 169.2, 136.1, 131.7, 124.7,
124.5, 116.3, 110.2, 40.0, 35.9, 26.9, 26.2, 26.0, 23.7, 21.0,
18.0, 16.4; MS (70 eV) m/z 262 (32), 151 (73), 133 (91), 109
(90), 69 (100), 43 (80). 22: Oil; IR (film) n 2961, 2918,
1
2856, 1756 (OCOCH3), 1451, 1368, 1260, 1213, 1098 cmK1
;
2855, 1756 (OCOCH3), 1448, 1368, 1214, 1099 cmK1; H
1H NMR (300 MHz, CDCl3) d 5.03 (tm, JZ7.1 Hz, 1H, H-
30), 2.20–2.00 (m, 2H), 2.05 (s, 3H, OCOCH3), 2.00–1.64
(m, 2H), 1.58 (s, 3H), 1.51 (s, 3H), 1.42 (s, 3H), 1.30–1.13
(m, 4H), 1.06–0.98 (m, 2H, H-1, H-6), 0.93 (s, 3H, H-8); 13C
NMR (75 MHz, CDCl3) d 169.9 (OCOCH3), 141.4 (C-2),
131.7 (C-40), 125.4 (C-30), 122.9 (C-3), 30.4 (C-4), 30.2
(C-20), 29.0 (C-7), 26.1 (C-9), 25.7 (C-10), 25.6 (C-6), 250.5
(C-8), 24.4 (C-1), 21.3 (OCOCH3), 18.3 (C-5), 17.8 (C-6 ),
16.4 (C-50); MS (70 eV) m/z 262 (MC, 12), 220 (63), 177
(17), 164 (13), 151 (42), 135 (100), 133 (5), 123 (18), 109
(44), 95 (20), 83 (11), 43 (38). Anal. Calcd for C17H26O2: C,
77.81; H, 9.99. Found: C, 77.76; H, 10.03.
NMR (200 MHz, CDCl3) d 4.98 (tm, JZ7.1 Hz, 1H, H-30),
2.20–1.65 (m, 2H, H-20), 2.25–2.08 (m, 1H), 2.06 (s, 3H,
OCOCH3), 2.00–1.85 (m, 2H),1.78–1.62 (m, 1H), 1.57 (s,
3H, H-50), 1.50 (s, 3H, H-60), 1.44 (s, 3H, H-9), 1.22–1.05
(m, 2H), 1.03–0.98 (m, 2H, H-1, H-6), 0.86 (s, 3H, H-8); 13C
NMR (75 MHz, CDCl3) d 169.0 (OCOCH3), 140.7 (C-2),
130.7 (C-40), 124.1 (C-30), 118.8 (C-3), 41.6 (C-4), 29.2
(C-20), 28.5 (C-7), 25.2 (C-10), 25.0 (C-9), 23.5 (C-6), 220.7
(C-1), 20.4 (OCOCH3), 17.1 (C-5), 17.0 (C-50), 15.6 (C-6 ),
12.4 (C-8); MS (70 eV) m/z 262 (MC, 4), 220 (47), 177 (13),
164 (10), 149 (27), 135 (100), 121 (30), 109 (56), 41 (82).
Anal. Calcd for C17H26O2: C, 77.82; H, 9.99. Found: C,
77.58; H, 9.67.
3.5.3. (6E)-3,7,11-Trimethyl-6,10-dodecadien-1-yn-3-yl
acetate (18).10 To a solution of geranyl acetone (0.5 g,
2.6 mmol) in dry THF/diethyl ether (1:1) (2 mL) was added
dropwise ethynylmagnesium bromide (6.5 mL, 3.1 mmol,
0.5 M in THF), at rt, in anhydrous diethyl ether (5 mL),
under argon. The reaction mixture was stirred at rt for 4 h.
Then water (20 mL) was added to quench the reaction and
the mixture was extracted with diethyl ether (2!3 mL). The
combined organic layers were washed with brine and dried
over anhydrous Na2SO4. The solvent was evaporated under
vacuum. Purification by flash chromatography (EtOAc/
hexane, 2:98) gave unreacted starting material (91 mg) and
the known derivative (6E)-3,7,11-trimethyl-1-dodeca-6,10-
dien-1-yn-3-ol (0.325 g, 70% yield) [1H NMR (200 MHz,
CDCl3) d 5.08 (m, 2H), 2.36 (d, JZ2.0 Hz, 1H), 2.30–1.82
(m, 8H), 1.60 (s, 3H), 1.59 (s, 3H), 1.55 (s, 1H, OH), 1.50 (s,
3H), 1.39 (s, 3H)]. Following the general protocol for the
esterification reaction, to a solution of (6E)-3,7,11-
trimethyl-1-dodeca-6,10-dien-1-yn-3-ol (0.3 g, 1.36 mmol)
in dry pyridine (5 mL), DMAP (32.2 mg, 0.27 mmol) and
acetic anhydride (208.1 mg, 0.28 mL, 2.04 mmol) were
added. The reaction mixture was stirred 24 h at rt. The
solvent was evaporated under vacuum and the crude was
purified by flash chromatography (EtOAc/hexane, 0.4:99.6)
to give compound 18 (150 mg, 63% yield) as a colorless oil,
that showed spectroscopic data [1H NMR (200 MHz,
CDCl3) d 5.03 (m, 2H, H-6, H-10), 2.46 (d, JZ1.7 Hz,
1H, H-1), 2.18–1.60 (m, 8H), 1.93 (s, 3H, OCOCH3), 1.58
(s, 6H), 1.52 (s, 6H)] in agreement with the structure of this
known product.10
3.5.5. 3-Methyl-hept-6-en-1-yn-3-yl acetate (23).6b
A
solution of of 6-hexene-2-one (0.50 g, 5.1 mmol) in a
mixture of dry THF/diethyl ether (1:1) (4 mL) was added
dropwise, at rt, to a solution of ethynylmagnesium bromide
(13 mL, 6.1 mmol, 0.5 M in THF) in anhydrous diethyl
ether (15 mL), under argon. The reaction mixture was
stirred at rt for 3 h. Then water (20 mL) was added to
quench the reaction and the mixture was extracted with
diethyl ether (2!3 mL). The combined organic layers were
washed with brine and dried over anhydrous Na2SO4. The
solvent was evaporated under vacuum. Purification by flash
chromatography (EtOAc/hexane, 5: 95) gave 3-methyl-
hept-6-en-1-yn-3-ol (0.32 g, 50% yield) [1H NMR
(200 MHz, CDCl3) d 5.76 (ddt, JZ6.6 Hz, JZ10.0 Hz,
JZ17.2 Hz, 1H), 5.01 (dm, JZ17.2 Hz, 1H), 4.86 (dm, JZ
10 Hz, 1H), 2.35 (s, 1H), 2.34–2.09 (m, 2H), 2.07 (br s, 1H),
1.69–1.61 (m, 2H), 1.39 (s, 3H)]. Following the general
method for the esterification reaction, to a solution of
3-methyl-hept-6-en-1-yn-3-ol (200 mg, 1.60 mmol) in dry
pyridine (4 mL), DMAP (39 mg, 0.32 mmol) and acetic
anhydride (0.32 mg, 0.36 mL, 2.42 mmol) were added. The
reaction mixture was stirred 12 h at rt. The solvent was
evaporated under vacuum and the crude was purified by
flash chromatography (EtOAc/hexane, 0.8:99.2) to furnish
acetate 23 (180 mg, 67% yield) as a colorless oil, that
spectroscopic data [1H NMR (200 MHz, CDCl3) d 5.72 (ddt,
JZ6.6 Hz, JZ10.0 Hz, JZ17.2 Hz, 1H, H-6), 4.906 (dm,
JZ17.2 Hz, 1H, H-7), 4.87 (dm, JZ10 Hz, 1H, H-7 ), 2.45
(s, 1H, H-1), 2.25–2.06 (m, 2H, H-5), 1.92 (s, 3H,
OCOCH3), 2.00–1.86 (m, 1H, H-4), 1.84–1.69 (m, 1H,
H-40), 1.57 (s, 3H, H-8)] in good agreement with the
structure of this known product.6b
3.5.4. (6E)-3,7,11-Trimethyl-1,2,6,10-dodecatetraen-1-yl
acetate (21).11 and (1S*,6R*,7S*)-3,7-dimethyl-7-(4-
methyl-3-pentenyl)bicyclo[41.0]hept-2-en-2-yl acetate
(22). Following the general procedure for the PtCl2-
catalyzed cycloisomerisation reaction, to a degassed
solution of compound (18) (120 mg, 0.458 mmol) in dry
toluene (18 mL) PtCl2 (6.1 mg, 0.023 mmol) was added.
3.5.6. 3-Methylbicyclo[4.1.0] hept-2-en-2-yl acetate (24).
Following the general procedure for the PtCl2-catalyzed
cycloisomerisation reaction, to a degassed solution of
1-ethynyl-1-methyl-4-pentenyl acetate (23) (140.8 mg,

4802
S. Anjum, J. Marco-Contelles / Tetrahedron 61 (2005) 4793–4803
2003, 1, 215–236. (d) Aubert, C.; Buisine, O.; Malacria, M.
0.81 mmol) in dry toluene (32 mL), PtCl2 (10.8 mg,
0.04 mmol) was added. The reaction mixture was stirred
for 18 h at rt. Purification by flash chromatography (EtOAc/
hexane, 0.8:99.2) afforded the expected product 24
(140.0 mg, 99% yield): Oil; IR (film) n 3074, 3005, 2919,
2859, 1755 (OCOCH3), 1698, 1445, 1368, 1320, 1228,
´
Chem. Rev. 2002, 102, 813–834. (e) Mendez, M.; Mamane, V.;
Fu¨rstner, A. Chemtracts 2003, 16, 397–425.
2. (a) Trost, B. M. Science 1991, 254, 1471–1477. (b) Trost,
B. M. Acc. Chem. Res. 1990, 23, 34–42.
3. (a) Trost, B. M.; Toste, F. D. J. Am. Chem. Soc. 2002, 124,
5025–5036. (b) Trost, B. M.; Hashmi, A. S. K. Angew. Chem.,
Int. Ed. 1993, 32, 1085–1087. (c) Trost, B. M.; Hashmi,
A. S. K. J. Am. Chem. Soc. 1994, 116, 2183–2184. (d) Chatani,
N.; Morimoto, T.; Muto, T.; Murai, S. J. Am. Chem. Soc. 1994,
116, 6049–6050. (e) Oi, S.; Tsukamoto, I.; Miyano, I.; Inoue,
Y. Organometallics 2001, 20, 3704–3709. (f) Dankwardt,
J. W. Tetrahedron Lett. 2001, 42, 5809–5812. (g) Mamane, V.;
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1214 cmK1; H NMR (300 MHz, CDCl3) d 2.07 (s, 3H,
1
OCOCH3), 1.84–1.54 (m, 4H, H-4, H-5), 1.38 (br s, 3H,
H-8), 1.38–1.18 (m, 1H, H-6), 1.07 (td, JZ4.6 Hz, JZ
8.5 Hz, 1H, H-1), 0.67 (dt, JZ4.6 Hz, JZ8.0 Hz, 1H, H-7),
0.59 (m, 1H, H-70); 13C NMR (75 MHz, CDCl3) d 169.6
(OCOCH3), 143.4 (C-2), 115.3 (C-3), 26.2 (C-4), 21.1
(OCOCH3), 19.6 (C-5), 16.5 (C-8), 14.6 (C-6), 12.3 (C-1),
10.4 (C-7). Anal. Calcd for C10H14O2: C, 72.26; H, 8.49.
Found: C, 72.33; H, 8.25.
3.5.7. 2-Methyl bicyclo[4.1.0]heptan-2-one (25).13
Following the general method for the methanolysis of the
enol esters, to a solution of 3-methylbicyclo[4.1.0]hept-2-
en-2-yl acetate (24) (200 mg, 1.15 mmol) in methanol
(22 mL, 0.05 M) solid potassium carbonate (225.3 mg,
2.29 mmol) was added. The reaction mixture was stirred
at rt for 18 h, quenched by adding brine (25 mL), extracted
with diethyl ether and dried over anhydrous Na2SO4.
Purification by flash column chromatography (EtOAc/
hexane, 2:98) afforded 2-methyl bicycle[4.1.0]heptan-2-
one (25) (87 mg, 61% yield), isolated as an inseparable
mixture of cis/trans diastereomers in a 1.5:1 ratio, which
showed identical spectroscopic to those described for these
isomers in literature:13 Oil; IR (film) n 3081, 3015, 2960,
2931, 2872, 1688, 1456, 1376, 1351, 1214, 1192 cmK1; 1H
NMR (200 MHz, CDCl3) d 2.20–1.72 (m, 2H), 1.70–15.2
(m, 3H), 1.32–1.12 (m, 2H), 0.98 (d, JZ7.0 Hz, H-8, major
trans isomer), 0.91 (d, JZ7.0 Hz, H-8, minor trans isomer),
0.94–0.78 (m, 2H); 13C NMR (75 MHz, CDCl3) d (major cis
isomer) 211.3 (C-2), 42.5 (C-3), 25.5 (C-6), 25.0 (C-4), 21.8
(C-5), 16.6 (C-1), 16.6 (C-8), 8.5 (C-7); (minor trans
isomer) 212.8 (C-2), 39.2 (C-3), 30.0 (C-4), 20.9 (C-5), 19.6
(C-6), 14.2 (C-1), 16.4 (C-8), 15.6 (C-7); GLC/MS m/z
(major cis isomer) (retention time: 10.99 min) 124 (MC, 36)
109 (15), 95 (12), 81 (62), 67 (25), 54 (100), 51 (7) 39 (50);
(minor trans isomer) (retention time: 11.22 min) m/z 124
(MC, 34) 109 (13), 97 (8), 95 (11), 81 (60), 67 (21), 54
(100), 39 (50).
´ ´
Martın-Matute, B.; Nevado, C.; Cardenas, D. J.; Echavarren,
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Acknowledgements
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The experimental part of this work has been carried out by
S.A., since April 2002 to December 2002, in the Laboratorio
de Radicales Libres (IQOG, CSIC, Madrid, Spain), based on
an independent and original project. JMC thanks MCyT by
financial support and to Johnson Matthey PLC for a
generous gift of PtCl2.
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References and notes
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communication (Fu¨rstner, A.; Hannen, P. Chem. Commun.
2004, 2546–2547) on the same subject, describing the AuCl3-
catalyzed cycloisomerization reaction of similar propargylic
carboxylates.
16. During the preparation of this manuscript we were aware of a