Cobalt-catalysed [6+2] cycloaddition of internal alkynes and terminal alkenes with cycloheptatriene

Article abstract of DOI:10.1055/s-0029-1216900

The cobalt-catalysed [6+2] cycloaddition of cycloheptatriene with internal alkynes as well as with terminal alkenes is described. The cycloaddition process is most efficiently catalysed by cobalt dibromide[bis(triisopropylphosphite)] complexes in dichloro

Full text of DOI:10.1055/s-0029-1216900

PAPER
3305
Cobalt-Catalysed [6+2] Cycloaddition of Internal Alkynes and Terminal
Alkenes with Cycloheptatriene
C
obalt-Catalysed[
e
6+2] Cyclo
r
additionhard Hilt,* Anna Paul, Christoph Hengst
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein Straße, 35043 Marburg, Germany
Fax +49(6421)2825677; E-mail: Hilt@chemie.uni-marburg.de
Received 12 May 2009
Et CoBr2(P(Oi-Pr)3)2
Abstract: The cobalt-catalysed [6+2] cycloaddition of cyclohep-
tatriene with internal alkynes as well as with terminal alkenes is de-
Zn, ZnI2, CH2Cl2
Et
+
scribed. The cycloaddition process is most efficiently catalysed by
cobalt dibromide[bis(triisopropylphosphite)] complexes in dichlo-
romethane as the solvent of choice. In the cobalt-catalysed reaction
of cycloheptatriene with norbornene an unexpected tricyclic [2+2]
cycloaddition product was isolated in excellent yields.
r.t., 12 h
Et
Et
1
2b
3b
Scheme 2 Cobalt-catalysed [6+2] cycloaddition of internal alkynes
Key words: alkyne, alkene, cobalt, cycloaddition, dienes
or terminal alkenes
[2+2+2] cyclotrimerisation of terminal as well as internal
alkynes under reductive conditions.3b Accordingly, in the
presence of a 1,3-diene or a cycloheptatriene as starting
material a [4+2] or a [6+2] cycloaddition process becomes
more favourable compared to the [2+2+2] cyclotrimerisa-
tion reaction pathway. In order to achieve further optimi-
sation of the reaction and to minimise the amount of side
products, a limited number of solvents and ligands were
screened in the reaction of cycloheptatriene with hex-1-
ene as test substrate to generate 5a (see Scheme 4; R = n-
Bu). We chose this test system although in GCMS analy-
sis three isomers (most likely: endo/exo-[6+2] cyclisation
isomers of 5a and the hydrovinylation product) were de-
tectable. Separation of these hydrocarbon molecules by
column chromatography was very tedious with only lim-
ited success because of their highly unpolar nature.
The application of cobalt complexes in cycloaddition re-
actions and other carbon–carbon bond formation processes
is well documented.1 While the predominant application
of cobalt catalysts lies in the formation of five-2 and six-
membered-ring systems,3 recent reports describe the ap-
plications of cobalt catalysts for the formation of four-4 as
well as eight-membered-ring systems.5 Only a few years
ago Buono established a methodology for the first exam-
ple of a cobalt-catalysed [6+2] cycloaddition process util-
ising cycloheptatriene6 (Scheme 1) as well as cycloocta-
tetraene or cyclooctatriene7 as starting materials in cobalt-
catalysed cycloadditions applying mostly terminal
alkynes such as phenylacetylene as starting materials.
Ph
CoI2(ligand)
Zn, ZnI2, (CH2Cl)2
Ph
In a brief survey of the solvents which had been most ef-
ficient over the course of our previous investigations con-
cerning cobalt-catalysed reactions utilising triisopropyl
phosphite as ligand, dichloromethane proved to be the sol-
vent of choice resulting in a quantitative yield of 5a
(>99%). Other solvents such as THF or acetonitrile gave
inferior results. In the investigation concerning the appli-
cable ligand in the reaction of cycloheptatriene with hex-
1-ene for the formation of 5a, we focused mainly on
ligand systems, which had been used successfully before
in other investigations.3b,4a,5a Among these, diphosphine-
type ligands such as bis-diphenylphosphinomethane
(dppm) and 1,2-bis-diphenylphosphinoethane (dppe)
were among the few successfully tested ligands yielding
5a in 51% and 76%, respectively, within 12 hours reaction
time. Other bidentate diphenylphosphino-type ligands
with a longer chain in between the two donor centres, such
as dppp, dppb, dpph, and dppf were found to be unreactive
under the present reaction conditions.8 Also, triphe-
nylphosphine and triphenylarsine were unsuitable ligands
in this transformation whereas 2-pyridylmethyldiphe-
nylphosphine gave traces of the desired product 5a. Dis-
ulfide ligands such as ethylenediphenyl sulfide, a ligand
+
40 °C, 20 h
1
2a
3a
Scheme 1 First cobalt-catalysed [6+2] cycloaddition reaction
Our own research led us primarily to an unprecedented
cobalt-catalysed formation of an eight-membered ring
system by a [4+2+2] cycloaddition process. Simulta-
neously we found a very reactive catalyst system, which
performed the [6+2] cycloaddition as outlined in
Scheme 1 when internal alkynes, such as hex-3-yne
(Scheme 2), were used leading to the generation of
bridged eight-membered cyclooctatriene derivatives of
type 3.
As we have shown recently, cobalt phosphine (or phos-
phite) based catalyst systems are of limited use for the
SYNTHESIS 2009, No. 19, pp 3305–3310
Advanced online publication: 10.07.2009
DOI: 10.1055/s-0029-1216900; Art ID: Z09709SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
0
9

3306
G. Hilt et al.
PAPER
type which proved to be very interesting in the [2+2+2]
cyclotrimerisation reaction,3b or diimine-type ligands,
such as bis-cyclohexylethylenediimine, or isopropyl-2-
pyridin-2-ylmethyleneamine gave no desired conversion
to 5a.5a
Table 2 Cobalt-Catalysed [6+2] Cycloaddition of Internal Alkynes
with Cycloheptatrienea
Entry
1
R1
R2
Product 3
3a
Yield (%)
95
Ph
Ph
A selection of phosphite ligands were also tested in the
conversion of cycloheptatriene with internal alkynes 2
(according to Scheme 3). The results for the phosphite
screening are summarised in Table 1.
2
Et
Et
3b
86
3
CH2OMe
CO2Me
Ph
CH2OMe
CO2Me
CH2OTMS
CH2OTMS
CH2OAc
Me
3c
42
4
3d
21
Table 1 Cobalt-Catalysed [6+2] Cycloaddition of Internal Alkynes
5
3e
66
with Cycloheptatriene Utilising Phosphite Ligandsa
6
Me
3f
53
Entry
Alkyne
Ligand
Yield (%)
7
Me
3g
15
1
2
3
P(OMe)3
P(OEt)3
P(Oi-Pr)3
91
88
94
8
Et
3h
78
TMS
TMS
9
Ph
Me
3i
28
4
5
6
P(OMe)3
P(OEt)3
P(Oi-Pr)3
60
60
63
10
11
12
13
14
Ph
Et
3j
36
Me
Me
CO2Et
Et
Ph
CO2Et
CO2Et
C≡CTMS
C≡CPh
3k
11
7
8
9
P(OMe)3
P(OEt)3
P(Oi-Pr)3
86
96
78
Me
3l
63
TMS
Ph
3m
3n
94
a Reaction conditions: Alkyne (1.0 mmol), cycloheptatriene (1.0
mmol), CoBr2 (0.05 mmol), ligand (0.10 mmol), Zn (0.10 mmol),
ZnI2 (0.10 mmol), CH2Cl2 (1 mL), r.t., 12 h.
10
a Reaction conditions: Alkyne (1.0 mmol), cycloheptatriene (1.0
mmol), CoBr2 (0.05 mmol), P(Oi-Pr)3 (0.10 mmol), Zn (0.10 mmol),
ZnI2 (0.10 mmol), CH2Cl2 (1 mL), 12 h, r.t.
Accordingly, transformations of internal alkynes 2 were
performed with a catalyst system consisting of an in situ
generated cobalt complex derived from CoBr2 (5 mol%),
the ligand P(Oi-Pr)3 (10 mol%), zinc powder (10 mol%),
and zinc iodide (10 mol%) in dichloromethane as solvent
at ambient temperature for 12 hours (Scheme 3). The con-
versions of equimolar amounts of internal symmetrical as
well as unsymmetrical alkynes 2 and cycloheptatriene
(1.0 mmol scale) were conducted under these conditions
for the formation of products of type 3 and the results are
summarised in Table 2.
In an earlier study concerning cobalt-catalysed [4+2+2]
cycloadditions, we found that the application of iron pow-
der as additive gave the desired eight-membered products
with increased chemoselectivity by reducing the amount
of cyclotrimerisation by-products. In contrast to these re-
actions, the addition of iron powder in the present [6+2]
cycloaddition reaction did not result in higher yields or in-
creased chemoselectivity.
The application of terminal alkenes was also possible in
the cobalt-catalysed [6+2] cycloaddition when isopropyl
phosphite was used as ligand (Scheme 4). From the reac-
tion of hex-1-ene, which was already mentioned above,
besides the desired cycloadduct 5a, also the side product
6 (R = Bu) of a cobalt-catalysed 1,4-hydrovinylation reac-
tion could be isolated and characterised after tedious col-
umn chromatography in pure form.
R1
CoBr2 (5 mol%)
P(Oi-Pr)3 (10 mol%)
R1
+
Zn powder (10 mol%)
ZnI2 (10 mol%)
CH2Cl2, r.t., 12 h
R2
R2
1
2
3
Scheme 3 Cobalt-catalysed [6+2] cycloaddition of internal alkynes
CoBr2(P(Oi-Pr)3)2
Zn, ZnI2, CH2Cl2
The varying yields are mostly a reflection of the tendency
of the alkyne to undergo a cobalt-catalysed cyclotrimeri-
sation reaction. Generally, the cyclotrimerisation products
can be purified by column chromatography on silica gel.
Those substrates whose cyclotrimerisation tendency is
small gave good to excellent yields. Sterically hindered
alkynes such as 1,2-bis(trimethylsilyl)acetylene did not
react under the present reaction conditions.
+
r.t., 12 h
R
5
R
1
4
R
6
Scheme 4 Cobalt-catalysed [6+2] cycloaddition of terminal alkenes
Synthesis 2009, No. 19, 3305–3310 © Thieme Stuttgart · New York

PAPER
Cobalt-Catalysed [6+2] Cycloaddition
3307
Although many different alkenes were tested, only a few All reactions were carried out under an inert atmosphere (nitrogen
or argon) using standard Schlenk techniques in flame-dried glass-
of them gave analytically pure compounds for a full char-
ware. CH2Cl2 was distilled over P4O10, MeCN over CaH2, and THF
acterisation. These results are summarised in Table 3.
over sodium/benzophenone. ZnI2 was dried in vacuo at 150 °C prior
to use. Commercially available materials were used without further
Table 3 Cobalt-Catalysed [6+2] Cycloaddition of Terminal Alk-
purification. NMR spectra were recorded on Bruker Avance 300 or
enes with Cycloheptatriene
DRX 500 (1H: 300 MHz or 500 MHz, 13C: 75 MHz or 125 MHz)
Entry
R
Product 5
Yield (%)a
spectrometers using TMS as internal standard (d = 0 ppm) unless
otherwise noted. IR spectra were recorded on a Bruker IFS 200 In-
terferometer or a Nicolet Magna IR 750 spectrometer. MS and GC/
MS spectra were measured on a Hewlett Packard 6890 GC system
including a Hewlett Packard 5973 mass selective detector. For
(high-resolution) mass spectra, a Finnigan MAT 95S and a Finnigan
LTQ (ESI, HRMS) spectrometer were used. Analytical thin-layer
chromatography was performed on Merck silica gel 60 F254. For
column chromatography, Merck silica gel 60 (230–400 mesh
ASTM) was used.
1
2
3
4
Bu
5a
5b
5c
5d
99b
83c
92
OBu
OAc
CH2N(Phth)
99
a Alkene (1.0 mmol), cycloheptatriene (1.0 mmol), CoBr2 (0.05
mmol), P(Oi-Pr)3 (0.10 mmol), Zn (0.10 mmol), ZnI2 (0.10 mmol),
CH2Cl2 (1 mL), 12 h, r.t.
7,8-Diphenylbicyclo [4.2.1]nona-2,4,7-triene (3a); Typical Pro-
cedure
b A mixture of four isomers was detected by GC/GCMS consisting of
57% 5a, 30% 6, and two isomers in minor amounts.
c Mixture of four isomers. An analytically pure sample could not be
isolated.
To a suspension of CoBr2 (22 mg, 0.1 mmol, 5 mol%), P(Oi-Pr)3 (21
mg, 0.2 mmol, 10 mol%), Zn powder (13 mg, 0.2 mmol, 20 mol%),
and ZnI2 (64 mg, 0.2 mmol, 20 mol%) in CH2Cl2 (1.0 mL) were
added cycloheptatriene (92 mg, 1.0 mmol, 1.0 equiv) and diphenyl-
acetylene (178 mg, 1.0 mmol, 1.0 equiv) under argon. The reaction
mixture was stirred at r.t. for 12 h. The reaction mixture was passed
through a pad of silica using pentane–Et2O (10:1) as eluent. The sol-
vents were removed and the crude product was purified by flash
chromatography using pentane–Et2O as eluent.
Besides the substrates shown in Table 3, silyl-protected
allylic alcohols, allylbenzene derivatives, and allyl aryl
ethers were also tested and in these cases mixtures of 3–5
isomers could be detected by GCMS analysis and isolated
in 14–59% yields. The best results were obtained for vinyl
ethers as well as for some terminal alkenes.
1H NMR (300 MHz, CDCl3): d = 7.42–7.28 (m, 10 H), 6.50–6.40
(m, 2 H), 6.12–6.04 (m, 2 H), 3.85–3.77 (m, 2 H), 2.82–2.70 (m, 1
H), 2.04–1.96 (m, 1 H).
A rational for the other isomers detected by GCMS anal-
ysis, which were neither isolated nor characterised, was
encountered when norbornene was used as starting mate-
rial. Under these conditions out of many possible reaction
pathways such as the herein described [6+2] cycloaddi-
tion, or a possible [4+2]/[2+2] cycloaddition, or 1,4-hy-
drovinylation reaction only a single product 8 was
generated in excellent 96% yield. Two-dimensional NMR
analysis and NOESY spectra revealed that product 8 was
produced by a formal [2+2] cycloaddition as a single ste-
reoisomer.
13C NMR (75 MHz, CDCl3): d = 139.3, 136.8, 136.1, 129.2, 128.1,
126.6, 124.8, 49.4, 30.6.
MS (EI): m/z (%) = 270 (100, M+), 255 (26), 239 (16), 192 (25), 178
(41), 165 (18), 115 (17), 91 (16).
7,8-Diethylbicyclo[4.2.1]nona-2,4,7-triene (3b)
1H NMR (300 MHz, CDCl3): d = 6.24–6.14 (m, 2 H), 5.77–5.69 (m,
2 H), 3.11 (t, J = 6.9 Hz, 2 H), 2.22–1.98 (m, 6 H), 1.02 (t, J = 7.6
Hz, 6 H).
13C NMR (75 MHz, CDCl3): d = 140.5, 136.2, 123.8, 46.2, 31.1,
19.3, 14.6.
MS (EI): m/z (%) = 174 (M+, 47), 145 (100), 129 (18), 117 (75), 115
(25), 105 (24), 91 (35).
CoBr2 (5 mol%)
P(Oi-Pr)3 (10 mol%)
H
H
+
Zn powder (10 mol%)
ZnI2 (10 mol%)
7,8-Bis(methoxymethyl)bicyclo[4.2.1]nona-2,4,7-triene (3c)
IR (KBr): 3017, 2925, 2817, 1672, 1452, 1377, 1164, 1099, 958,
910, 798, 695 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.16 (dt, J = 3.3, 8.0 Hz, 2 H),
5.77 (qd, J = 3.6, 7.0 Hz, 2 H), 4.12 (d, J = 12.2 Hz, 2 H), 3.90 (d,
J = 12.3 Hz, 2 H), 3.34–3.27 (m, 2 H), 3.25 (s, 6 H), 2.25–2.15 (m,
1 H), 1.58 (d, J = 11.4 Hz, 1 H).
H
H
CH2Cl2, r.t., 12 h
96%
1
7
8
Scheme 5 Cobalt-catalysed [2+2] cycloaddition of cycloheptatriene
with norbornene
13C NMR (75 MHz, CDCl3): d = 139.5, 135.3, 124.5, 66.1, 57.8,
In summary, we were able to demonstrate that internal
alkynes are accepted substrates for the cobalt-catalysed
[6+2] cycloaddition when phosphite ligands are used. On
45.3, 30.1.
MS (EI): m/z (%) = 206 (M+, 14), 174 (59), 159 (21), 142 (33), 129
the other hand, the application of alkenes is limited to a (100), 115 (50), 91 (46).
few acceptable starting materials producing up to five iso-
mers. Finally, the reaction of norbornene with cyclohep-
tatriene gave a [2+2] cycloaddition tricyclic hydrocarbon
product in excellent yields.
HRMS: m/z calcd for C13H18O2: 206.1307; found: 206.1296.
Dimethyl Bicyclo[4.2.1]nona-2,4,7-trien-7,8-dicarboxylate (3d)
1H NMR (300 MHz, CDCl3): d = 6.19–6.11 (m, 2 H), 6.00–5.92 (m,
2 H), 3.74 (s, 6 H), 3.54 (t, J = 6.9 Hz, 2 H), 2.36–2.26 (m, 1 H),
1.60 (d, J = 11.8 Hz, 1 H).
Synthesis 2009, No. 19, 3305–3310 © Thieme Stuttgart · New York

3308
G. Hilt et al.
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HRMS (EI): m/z calcd for C12H16: 160.1252; found: 160.1260.
13C NMR (75 MHz, CDCl3): d = 165.1, 136.6, 132.6, 125.9, 52.1,
45.0, 29.8.
7-Methyl-8-phenylbicyclo[4.2.1]nona-2,4,7-triene (3i)
IR (film): 3053, 3017, 2925, 2854, 1948, 1717, 1681, 1598, 1492,
1442, 1376, 1319, 1217, 1175, 1031, 975, 913, 838, 761 cm–1.
MS (EI): m/z (%) = 234 (M+, 58), 207 (16), 203 (38), 175 (21), 143
(35), 131 (26), 115 (100), 91 (28).
Trimethyl[(8-phenylbicyclo[4.2.1]nona-2,4,7-trien-7-yl)meth-
oxy]silane (3e)
IR (film): 3065, 3020, 2955, 2169, 1949, 1722, 1681, 1598, 1573,
1493, 1444, 1408, 1375, 1315, 1251, 1171, 1069, 873, 842, 760,
725 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.33–7.19 (m, 5 H), 6.27–6.14 (m,
2 H), 5.88–5.77 (m, 2 H), 4.40 (d, J = 12.7 Hz, 1 H), 4.15 (d,
J = 12.7 Hz, 1 H), 3.57 (t, J = 7.1 Hz, 1 H), 3.50 (t, J = 7.0 Hz, 1 H),
2.46–2.38 (m, 1 H), 1.69 (d, J = 11.4 Hz, 1 H), 0.07 (s, 9 H).
1H NMR (300 MHz, CDCl3): d = 7.31–7.30 (m, 4 H), 7.23–7.16 (m,
1 H), 6.31–6.22 (m, 2 H), 5.87–5.76 (m, 2 H), 3.46 (t, J = 6.9 Hz, 1
H), 3.19 (t, J = 7.0 Hz, 1 H), 2.44–2.35 (m, 1 H), 1.87 (s, 3 H), 1.69
(d, J = 11.2 Hz, 1 H).
13C NMR (75 MHz, CDCl3): d = 140.7, 139.2, 137.0, 134.9, 133.0,
128.8, 127.9, 126.1, 124.6, 124.0, 49.9, 48.2, 30.5, 12.8.
MS (EI): m/z (%) = 208 (M+, 100), 193 (97), 178 (80), 165 (42), 152
(13), 139 (4), 129 (12), 115 (48), 103 (4), 91 (25), 82 (3), 77 (7), 65
(5).
13C NMR (75 MHz, CDCl3): d = 139.6, 136.3, 136.0, 135.7, 129.1,
128.0, 126.8, 124.5, 124.4, 57.1, 48.6, 44.9, 30.3, –0.4.
HRMS (EI): m/z calcd for C16H16: 208.1252; found: 208.1267.
MS (EI): m/z (%) = 296 (M+, 52), 281 (6), 268 (2), 255 (3), 242 (22),
229 (3), 218 (3), 205 (44), 191 (33), 178 (29), 165 (37), 155 (12),
142 (4), 129 (22), 115 (29), 103 (13), 91 (43), 73 (100), 65 (4).
7-Ethyl-8-phenylbicyclo[4.2.1]nona-2,4,7-triene (3j)
IR (film): 3053, 3018, 2964, 2933, 2874, 2169, 1717, 1682, 1598,
1492, 1443, 1375, 1315, 1272, 1176, 1069, 981, 918, 846, 762, 721
cm–1.
1H NMR (300 MHz, CDCl3): d = 7.31–7.15 (m, 5 H), 6.26–6.16 (m,
2 H), 5.84–5.75 (m, 2 H), 3.42 (t, J = 6.9 Hz, 1 H), 3.31 (t, J = 6.9
Hz, 1 H), 2.40–2.11 (m, 3 H), 1.68 (d, J = 11.2 Hz, 1 H), 1.07 (dt,
J = 1.3, 7.5 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 140.2, 139.5, 139.4, 137.2, 134.4,
128.9, 127.9, 126.2, 124.3, 124.0, 48.4, 46.7, 30.8, 20.1, 14.3.
MS (EI): m/z (%) = 222 (M+, 59), 207 (10), 193 (100), 178 (77), 165
(40), 152 (11), 141 (4), 129 (13), 115 (53), 102 (3), 91 (38), 77 (8),
65 (5).
HRMS (EI): m/z calcd for C19H24OSi: 296.1596; found: 296.1581.
Trimethyl[(8-methylbicyclo[4.2.1]nona-2,4,7-trien-7-yl)meth-
oxy]silane (3f)
IR (film): 3016, 2955, 2873, 2169, 1718, 1680, 1562, 1444, 1409,
1378, 1315, 1251, 1170, 1086, 1050, 872, 842, 754, 728, 689 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.21–6.11 (m, 2 H), 5.75–5.68 (m,
2 H), 4.24 (d, J = 12.6 Hz, 1 H), 4.08 (d, J = 12.5 Hz, 1 H), 3.29 (t,
J = 7.0 Hz, 1 H), 2.97 (t, J = 6.9 Hz, 1 H), 2.23–2.15 (m, 1 H), 1.67
(s, 3 H), 1.54 (d, J = 11.3 Hz, 1 H), 0.09 (s, 9 H).
13C NMR (75 MHz, CDCl3): d = 140.9, 139.7, 134.4, 132.1, 124.3,
123.9, 56.5, 49.1, 44.2, 30.1, 11.2, -0.4.
HRMS (EI): m/z calcd for C17H18: 222.1409; found: 222.1408.
MS (EI): m/z (%) = 234 (M+, 11), 219 (6), 193 (2), 180 (4), 155 (4),
Ethyl 8-Phenylbicyclo[4.2.1]nona-2,4,7-triene-7-carboxylate
143 (21), 129 (80), 115 (17), 103 (13), 91 (23), 73 (100), 65 (5).
(3k)
IR (film): 3022, 2979, 2934, 1954, 1702, 1636, 1597, 1575, 1492,
1444, 1370, 1335, 1298, 1245, 1195, 1112, 1030, 864, 798, 761
cm–1.
1H NMR (300 MHz, CDCl3): d = 7.51–7.27 (m, 5 H), 6.32–6.24 (m,
1 H), 5.96–5.79 (m, 3 H), 3.94 (dq, J = 1.5, 7.1 Hz, 2 H), 3.57 (t,
J = 7.1 Hz, 1 H), 3.50 (t, J = 7.0 Hz, 1 H), 2.37–2.29 (m, 1 H), 1.59
(d, J = 11.6 Hz, 1 H), 0.97 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 165.1, 147.6, 136.4, 135.4, 132.9,
130.5, 128.7, 128.5, 127.7, 127.5, 126.9, 125.8, 124.2, 59.9, 50.3,
45.2, 29.5, 13.8.
HRMS (EI): m/z calcd for C14H22OSi: 234.1440; found: 234.1442.
(8-Methylbicyclo[4.2.1]nona-2,4,7-trien-7-yl)methyl Acetate
(3g)
IR (film): 3016, 2933, 2735, 1738, 1680, 1442, 1378, 1315, 1232,
1023, 975, 857, 839, 813, 755, 666 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.20–6.11 (m, 2 H), 5.80–5.70 (m,
2 H), 4.72 (d, J = 12.5 Hz, 1 H), 4.54 (d, J = 12.5 Hz, 1 H), 3.17 (t,
J = 7.3 Hz, 1 H), 3.02 (t, J = 7.0 Hz, 1 H), 2.24–2.15 (m, 1 H), 2.04
(s, 3 H), 1.74 (s, 3 H), 1.55 (d, J = 11.3 Hz, 1 H).
13C NMR (75 MHz, CDCl3): d = 171.0, 140.3, 139.1, 135.8, 129.3,
MS (EI): m/z = 266 (M+, 27), 237 (4), 219 (12), 207 (15), 193 (100),
178 (75), 165 (40), 152 (13), 139 (7), 128 (4), 115 (78), 91 (33), 77
(10), 65 (8).
124.6, 124.1, 58.8, 48.9, 44.8, 30.1, 21.0, 11.3.
MS (EI): m/z (%) = 204 (M+, 12), 162 (12), 144 (20), 129 (100), 115
(21), 105 (10), 91 (36), 77 (11), 65 (9).
HRMS (EI): m/z calcd for C18H18O2: 266.1307; found: 266.1314.
HRMS (EI): m/z calcd for C13H16O2: 204.1150; found: 204.1156.
Ethyl 8-Methylbicyclo[4.2.1]nona-2,4,7-triene-7-carboxylate
(3l)
7-Ethyl-8-methylbicyclo[4.2.1]nona-2,4,7-triene (3h)
IR (film): 2962, 2928, 2873, 2733, 2169, 1718, 1677, 1562, 1458,
1410, 1378, 1316, 1261, 1171, 1018, 800, 758 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.19 (td, J = 6.3, 12.4 Hz, 2 H),
5.77–5.68 (m, 2 H), 3.08 (t, J = 6.9 Hz, 1 H), 2.96 (t, J = 6.9 Hz, 1
H), 2.26–1.96 (m, 3 H), 1.64 (s, 3 H), 1.53 (d, J = 11.1 Hz, 1 H),
0.99 (t, J = 7.6 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 140.9, 140.4, 137.1, 129.4, 123.9,
123.6, 48.8, 46.0, 30.7, 19.3, 14.1, 11.0.
MS (EI): m/z (%) = 160 (M+, 48), 145 (34), 131 (100), 115 (25), 105
(10), 91 (47), 77 (12), 65 (9), 51 (5).
IR (film): 2961, 2924, 2852, 2169, 1944, 1708, 1644, 1562, 1462,
1411, 1374, 1335, 1262, 1217, 1054, 865, 801, 704, 664, 629 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.34–6.27 (m, 1 H), 6.11–6.05 (m,
1 H), 5.89–5.5.76 (m, 2 H), 4.17 (q, J = 7.1 Hz, 2 H), 3.47 (t, J = 7.1
Hz, 1 H), 3.19 (t, J = 7.1 Hz, 1 H), 2.24–2.15 (m, 1 H), 2.13 (s, 3 H),
1.54 (d, J = 11.5 Hz, 1 H), 1.28 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 165.6, 149.1, 141.2, 136.4, 125.8,
125.4, 123.5, 59.7, 50.6, 44.2, 29.2, 14.3, 13.7.
MS (EI): m/z = 204 (M+, 28), 189 (1), 175 (2), 159 (9), 147 (2), 131
(100), 115 (36), 103 (5), 91 (43), 77 (12), 65 (7), 53 (8).
HRMS (EI): m/z calcd for C13H16O2: 204.1150; found: 204.1160.
Synthesis 2009, No. 19, 3305–3310 © Thieme Stuttgart · New York

PAPER
Cobalt-Catalysed [6+2] Cycloaddition
3309
Trimethyl[8-(trimethylsilyl)bicyclo[4.2.1]nona-2,4,7-trien-7-
yl]ethynylsilane (3m)
2-(Bicyclo[4.2.1]nona-2,4-dien-7-ylmethyl)-1H-isoindole-
1,3(2H)-dione (5d)
IR (film): 3020, 2957, 2898, 2169, 2141, 1942, 1725, 1685, 1630,
IR (film): 3024, 2937, 2833, 1778, 1718, 1656, 1611, 1467, 1384,
1562, 1450, 1408, 1317, 1249, 1159, 985, 956, 824, 759 cm–1.
1311, 1263, 1198, 1132, 1085, 1015, 993, 954, 883, 791, 714 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.19–6.13 (m, 1 H), 5.91–5.79 (m,
1 H), 3.33 (t, J = 7.2 Hz, 1 H), 3.20 (t, J = 7.0 Hz, 1 H), 2.11–2.03
(m, 1 H), 1.49 (d, J = 11.5 Hz, 1 H), 0.18 (s, 9 H), 0.16 (s, 9 H).
13C NMR (75 MHz, CDCl3): d = 146.8, 137.6, 137.4, 125.4, 124.8,
124.5, 103.2, 95.8, 49.7, 48.3, 30.6, –0.13, –0.68.
MS (EI): m/z = 286 (M+, 99), 271 (29), 255 (2), 227 (1), 213 (16),
197 (91), 183 (66), 169 (6), 155 (12), 145 (7), 131 (4), 116 (9), 107
(4), 91 (39), 83 (7), 73 (100), 59 (6).
1H NMR (300 MHz, CDCl3): d = 7.82 (dd, J = 3.0, 5.5 Hz, 1 H),
7.70 (dd, J = 3.0, 5.5 Hz, 2 H), 6.85–6.69 (m, 2 H), 5.83–5.78 (m, 1
H), 5.54–5.49 (m, 1 H), 2.45–2.39 (m, 2 H), 2.32–2.27 (m, 1 H),
2.25–2.13 (m, 1 H), 2.05–1.93 (m, 1 H), 1.86–1.76 (m, 3 H), 1.59–
1.50 (m, 1 H).
13C NMR (75 MHz, CDCl3): d = 166.6, 134.2, 131.7, 131.3, 124.9,
123.3, 122.9, 117.9, 45.9, 40.0, 38.3, 35.7, 33.4, 31.2.
MS (EI): m/z (%) = 279 (M+, 16), 251 (3), 238 (1), 225 (1), 212
(100), 199 (3), 186 (8), 173 (1), 167 (1), 160 (2), 148 (1), 148 (1),
130 (10), 117 (2), 104 (10), 91 (5), 91 (5), 75 (5), 65 (5).
HRMS (EI): m/z calcd for C17H26Si2: 286.1573; found: 286.1568.
7-Phenyl-8-(phenylethynyl)bicyclo[4.2.1]nona-2,4,7-triene (3n)
IR (film): 3054, 3019, 2917, 2848, 2192, 1948, 1682, 1596, 1487,
1462, 1442, 1384, 1331, 1215, 1102, 1069, 1013, 912, 879, 845,
756 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.99–7.96 (m, 2 H), 7.49–7.45 (m,
2 H), 7.39–7.29 (m, 6 H), 6.41–6.27 (m, 2 H), 5.95–5.88 (m, 2 H),
3.82 (t, J = 7.0 Hz, 1 H), 3.53 (t, J = 7.1 Hz, 1 H), 2.53–2.44 (m, 1
H), 1.81 (d, J = 11.5 Hz, 1 H).
HRMS (EI): m/z calcd for C18H17NO2: 279.1259; found: 279.1256.
6-[(1E)-Hex-1-en-1-yl]cyclohepta-1,4-diene (6)
IR (film): 2956, 2930, 2871, 2169, 1723, 1632, 1562, 1457, 1379,
1263, 1175, 1048, 756, 667 cm–1.
1H NMR (300 MHz, CDCl3): d = 5.64 (dd, J = 4.4, 4.1 Hz, 2 H),
5.56–5.53 (m, 2 H), 5.38 (dd, J = 2.7, 5.5 Hz, 2 H), 3.06–2.99 (m, 1
H), 2.91–2.81 (m, 1 H), 2.74–2.64 (m, 1 H), 2.24–2.17 (m, 2 H),
1.96–1.90 (m, 2 H), 1.27–1.20 (m, 4 H), 0.82 (t, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 143.1, 139.0, 138.4, 134.5, 131.4,
128.3, 128.2, 128.1, 128.0, 127.6, 125.3, 124.7, 123.6, 115.6, 93.6,
87.1, 49.2, 46.4, 30.1.
13C NMR (75 MHz, CDCl3): d = 134.9, 133.6, 129.7, 129.6, 128.9,
127.0, 40.7, 33.4, 32.1, 31.7, 28.2, 22.1, 13.9.
MS (EI): m/z (%) = 294 (M+, 100), 278 (20), 265 (13), 252 (15), 239
(6), 226 (3), 215 (47), 202 (33), 189 (7), 178 (5), 165 (6), 152 (2),
139 (7), 126 (5), 115 (6), 91 (9), 77 (2).
MS (EI): m/z (%) = 176 (M+, 4), 161 (1), 147 (2), 133 (6), 128 (2),
119 (25), 110 (10), 105 (40), 98 (1), 91 (100), 79 (65), 67 (25), 55
(13).
HRMS (EI): m/z calcd for C23H18: 294.1409; found: 294.1404.
HRMS (EI): m/z calcd for C13H20: 176.1565; found: 176.1561.
7-Butylbicyclo[4.2.1]nona-2,4-diene (5a)
Tetracyclo[9.2.1.02,10.03,9]tetradeca-4,6-diene (8)
IR (KBr): 3021, 2949, 2869, 1725, 1606, 1477, 1457, 1437, 1293,
1180, 739, 691, 664 cm–1.
IR (film): 3018, 2954, 2925, 2869, 1718, 1671, 1455, 1412, 1378,
1310, 1261, 1241, 1217, 1183, 1092, 1001, 978, 857, 803 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.09 (t, J = 9.9 Hz, 1 H), 5.85–
5.70 (m, 2 H), 5.59–5.53 (m, 1 H), 2.68–2.52 (m, 2 H), 2.31–2.05
(m, 3 H), 2.02–1.94 (m, 1 H), 1.84 (d, J = 11.8 Hz, 1 H), 1.55–1.45
(m, 2 H), 1.40 (t, J = 7.5 Hz, 1 H), 1.36–1.29 (m, 2 H), 0.88 (t,
J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 141.3, 135.6, 126.0, 123.1, 57.3,
44.1, 42.2, 36.4, 33.4, 31.8, 29.9, 22.9, 14.1.
1H NMR (600 MHz, CDCl3): d = 6.00 (dt, J = 6.7, 10.5 Hz, 1 H),
5.93 (dd, J = 11.3, 3.7 Hz, 1 H), 5.85 (tdd, J = 1.5, 4.8, 10.5 Hz, 1
H), 5.71 (ddd, J = 11.3, 4.8, 2.5 Hz, 1 H), 2.62–2.57 (m, 1 H), 2.48–
2.44 (m, 1 H), 2.42 (dd, J = 11.7, 6.2 Hz, 1 H), 2.11–2.08 (m, 1 H),
2.03–2.01 (m, 1 H), 2.01–1.97 (m, 1 H), 1.97–1.95 (m, 1 H), 1.93–
1.90 (m, 1 H), 1.85–1.81 (m, 1 H), 1.41–1.39 (m, 1 H), 1.39–1.38
(m, 1 H), 1.21–1.18 (m, 1 H), 0.98–0.96 (m, 1 H), 0.96–0.94 (m, 1
H).
13C NMR (75 MHz, CDCl3): d = 139.8, 132.7, 128.7, 125.3, 54.3,
49.3, 47.9, 41.4, 38.8, 38.0, 33.3, 33.2, 27.9, 27.3.
MS (EI): m/z (%) = 186 (M+, 15), 171 (4), 157 (6), 145 (12), 129
MS (EI): m/z = 176 (M+, 18), 161 (1), 147 (2), 135 (4), 119 (9), 105
(13), 98 (3), 91 (100), 84 (1), 79 (61), 70 (7), 65 (11), 56 (22).
HRMS (EI): m/z calcd for C13H20: 176.1565; found: 175.1570.
(20), 117 (24), 104 (18), 92 (100), 79 (24), 65 (15).
Bicyclo[4.2.1]nona-2,4-dien-7-yl Acetate (5b)
IR (KBr): 3021, 2938, 1736, 1436, 1374, 1242, 1025, 703, 608
cm–1.
HRMS: m/z calcd for C14H18: 186.1409; found: 186.1413.
1H NMR (300 MHz, CDCl3): d = 6.06 (dd, J = 10.6, 8.6 Hz, 1 H),
5.94 (dd, J = 11.4, 7.9 Hz, 1 H), 5.77 (ddd, J = 11.5, 7.1, 0.8 Hz, 1
H), 5.64 (dd, J = 11.0, 7.1 Hz, 1 H), 5.05 (dd, J = 6.6, 2.4 Hz, 1 H),
2.79 (q, J = 8.5 Hz, 1 H), 2.65 (t, J = 6.9 Hz, 1 H), 2.29–2.13 (m, 2
H), 1.99 (s, 3 H, CH3), 2.00–1.90 (m, 1 H), 1.69 (d, J = 12.2 Hz, 1
H).
13C NMR (75 MHz, CDCl3): d = 170.3, 139.5, 133.0, 125.7, 123.3,
84.3, 46.5, 45.2, 37.3, 29.9, 21.3.
MS (EI): m/z (%) = 178 (M+, 19), 136 (3), 117 (60), 103 (6), 92
(100), 77 (13).
References
(1) For reviews on cobalt-catalyzed cycloaddition processes,
see: (a) Hess, W.; Treutwein, J.; Hilt, G. Synthesis 2008,
3537. (b) Omae, I. Appl. Organomet. Chem. 2008, 22, 149.
(c) Omae, I. Appl. Organomet. Chem. 2007, 21, 318.
(d) Aubert, C.; Betschmann, P.; Eichberg, M. J.; Gandon, V.;
Heckrodt, T. J.; Lehmann, J.; Malacria, M.; Masjost, B.;
Paredes, E.; Vollhardt, K. P. C.; Whitener, G. D. Chem. Eur.
J. 2007, 13, 7443. (e) Gandon, V.; Aubert, C.; Malacria, M.
Curr. Org. Chem. 2005, 9, 1699. (f) Malacria, M.; Aubert,
C.; Renaud, J. L. In Science of Synthesis: Houben-Weyl
HRMS: m/z calcd for C11H14O2: 178.0994; found: 178.0994.
Synthesis 2009, No. 19, 3305–3310 © Thieme Stuttgart · New York

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PAPER
(4) (a) For selected references for the [2+2] cycloaddition of
Methods of Molecular Transformations, Vol. 1; Lautens,
M.; Trost, B. M., Eds.; Thieme: Stuttgart, 2001, 439.
(g) Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901.
(h) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J.
Chem. Rev. 1996, 96, 635. (i) Lautens, M.; Klute, W.; Tam,
W. Chem. Rev. 1996, 96, 49.
alkynes to cyclobutadiene complexes, see: Treutwein, J.;
Hilt, G. Angew. Chem. Int. Ed. 2008, 47, 6811.
(b) Takanashi, K.; Lee, V. Y.; Ichinohe, M.; Sekiguchia, A.
Eur. J. Inorg. Chem. 2007, 35, 5471. (c) Chang, C.-P.;
Kultyshev, R. G.; Hong, F.-E. J. Organomet. Chem. 2006,
691, 5831. (d) Goswami, A.; Sraeb, T. H.; Rominger, F.;
Gleiter, R.; Siebert, W. Eur. J. Inorg. Chem. 2005, 4086.
(e) Kudinov, A. R.; Mutseneck, E. V.; Loginov, D. A.
Coord. Chem. Rev. 2004, 248, 571.
(2) For recent reviews covering the Pauson–Khand reaction,
see: (a) Omae, I. Appl. Organomet. Chem. 2009, 23, 91.
(b) Michelet, V.; Toullec, P. Y.; Genet, J.-P. Angew. Chem.
Int. Ed. 2008, 47, 4268. (c) Omae, I. Appl. Organomet.
Chem. 2008, 22, 149. (d) Shibata, T. Adv. Synth. Catal.
2006, 348, 2328.
(3) For recent selected examples of cobalt-catalysed
cyclotrimerisations of alkynes, see: (a) Geny, A.; Agenet,
N.; Iannazzo, L.; Malacria, M.; Aubert, C.; Gandon, V.
Angew. Chem. Int. Ed. 2009, 48, 1810. (b) Hilt, G.; Hengst,
C.; Hess, W. Eur. J. Org. Chem. 2008, 2293. (c) Hilt, G.;
Vogler, T.; Hess, W.; Galbiati, F. Chem. Commun. 2005,
1474. (d) Doszczak, L.; Fey, P.; Tacke, R. Synlett 2007,
753. (e) Chang, H. T.; Jeganmohan, M.; Cheng, C. H. Org.
Lett. 2007, 9, 505. (f) Saino, N.; Amemiya, F.; Tanabe, E.;
Kase, K.; Okamoto, S. Org. Lett. 2006, 8, 1439. (g) Wu, M.
S.; Shanmugasundaram, M.; Cheng, C. H. Chem. Commun.
2003, 718. (h) Yong, L.; Butenschön, H. Chem. Commun.
2002, 2852. (i) Sugihara, T.; Wakabayashi, A.; Nagai, Y.;
Takao, H.; Imagawa, H.; Nishizawa, M. Chem. Commun.
2002, 576.
(5) (a) Hilt, G.; Janikowski, J. Angew. Chem. Int. Ed. 2008, 47,
5243. (b) See also: Lee, S. I.; Park, S. Y.; Chung, Y. K. Adv.
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(6) Toselli, N.; Martin, D.; Achard, M.; Tenaglia, A.; Bürgi, T.;
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(7) Achard, M.; Mosrin, M.; Tenaglia, A.; Buono, G. J. Org.
Chem. 2006, 71, 2907.
(8) dppp: 1,3-bis(diphenylphosphino)propane;
dppb: 1,4-bis(diphenylphosphino)butane;
dpph: 1,6-bis(diphenylphosphino)hexane;
dppf: 1,1¢-bis(diphenylphosphino)ferrocene.
Synthesis 2009, No. 19, 3305–3310 © Thieme Stuttgart · New York