Rhodium-catalyzed intramolecular cycloaddition of cyclopropene-ynes triggered by cabon-carbon bond cleavage

Article abstract of DOI:10.3987/COM-08-S(N)92

In the presence of a catalytic amount of RhCI(PPh₃)₃, an intramolecular cycloaddition of cyclopropene-yne proceeded along with carbon-carbon bond cleavage of cyclopropene ring to give various bicyclic cyclopentadiene derivatives in good to high yield.

Full text of DOI:10.3987/COM-08-S(N)92

HETEROCYCLES, Vol. 76, No. 2, 2008
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HETEROCYCLES, Vol. 76, No. 2, 2008, pp. 1261 - 1270. © The Japan Institute of Heterocyclic Chemistry
Received, 2nd April, 2008, Accepted, 22nd May, 2008, Published online, 26th May, 2008. COM-08-S(N)92
RHODIUM-CATALYZED INTRAMOLECULAR CYCLOADDITION OF
CYCLOPROPENE-YNES TRIGGERED BY CABON-CARBON BOND
CLEAVAGE
Takanori Shibata,* Shunsuke Maekawa, and Kohei Tamura
Department of Chemistry and Biochemistry, School of Advanced Science and
Engineering, Waseda University, Shinjuku, Tokyo, 169-8555, Japan,
tshibata@waseda.jp
Dedicated to Prof. R. Noyori on the occasion of his 70th birthday
Abstract – In the presence of a catalytic amount of RhCl(PPh3)3, an
intramolecular cycloaddition of cyclopropene-yne proceeded along with
carbon-carbon bond cleavage of cyclopropene ring to give various bicyclic
cyclopentadiene derivatives in good to high yield.
INTRODUCTION
Generally, carbon-carbon single bond is stable and difficult to cleave under the mild reaction conditions,
however, in the case of compounds with small ring systems, the bond cleavage can be possible using
release of strain energy as driving force. From a organic synthetic point of view, three-membered
carbocycles are fascinating building blocks and many researchers have focused on the development of
unique and synthetically valuable transformations.1 Actually, oxidative addition of transition metal
complexes to cyclopropane and cyclopropene rings along with carbon-carbon single bond cleavage has
been reported2 and it was applied for various transition metal-catalyzed transformations.3
Also in the cycloaddition, cyclopropane ring is an important C3 unit along with the bond cleavage. For
examples, Wender comprehensively studied the reaction of vinylcyclopropane with alkynes and realized
Rh-catalyzed intra- and intermolecular [5+2] cycloaddition.4 Murakami reported an Ir-catalyzed [5+1]
cycloaddition of allenylcyclopropane with carbon monoxide,5 Saito did a Ni-catalyzed intermolecular
[3+2+2] cycloaddition of methylenecyclopropanes with two alkynes,6 and Lauten and Mascareñas
independently did
a
Pd- or Ru-catalyzed intramolecular [3+2] cycloaddition of
methylenecyclopropane-ynes.7 In all these reactions, however, conjugated or adjacent carbon-carbon

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HETEROCYCLES, Vol. 76, No. 2, 2008
double bond to cyclopropane facilitated the ring cleavage. The catalytic cycloaddition including the
cleavage of isolated cyclopropane ring has been scarce: Narasaka achieved a Rh-catalyzed [3+2+1]
cycloaddition of carbon-tethered cyclopropane-ynes with carbon monoxide in relatively harsh reaction
conditions.8
Compared with cyclopropanes, cyclopropenes are unexplored in cycloaddition. For example, the
photo-irradiated [3+2] cycloaddition with alkynes was reported, however, it was considered that [2+2]
cycloaddition and the following ring expansion proceeded along with the cleavage of cyclopropane ring.9
Thermal [3+2] cycloaddition of functionalized cyclopropenes, such cyclopropenone acetals10 and
ferrocenyl cyclopropenes, was disclosed.11 As for transition metal-catalyzed reaction, a Ni-catalyzed
[3+2] cycloadditions of a cyclopropenone with a diphenylketene12 and an unfunctionalized cyclopropene
with tolane13 were reported, but the yield was low and substrates were limited. A Rh-catalyzed
carbonylation of cyclopropenyl esters and 3-vinylcyclopropenes is a more practical example, which
proceeded under an atmospheric pressure of carbon monoxide to give α-pyrones and phenols,
respectively ([5+1] cycloaddition).14 A Ru-catalyzed reaction of cyclopropenones with alkynes under
pressurized conditions of carbon monoxide is also a successful example.15
We here disclosed a Rh-catalyzed intramolecular reaction of cyclopropene-ynes. This is a rare example of
catalytic cycloaddition including the cleavage of unfunctionalized cyclopropene ring.
RESULTS AND DISCUSSION
As a model substrate, we chose oxygen-tethered 3,3-dimethylcyclopropene-yne 1a and submitted it to
various reaction conditions (Table 1). In the presence of [RhCl(cod)]2 as a catalyst, cyclopropene-yne 1a
was consumed under the reflux condition in toluene to give complex mixture (entry 1). When
triphenylphosphine was added as a ligand, it was completely consumed even at 60 °C within 3 h and
bicyclic cyclopentadiene 2a was obtained but in low yield (entry 2). Electron-deficient triarylphosphine
gave the comparable results to those of triphenylphosphine (entry 3). Electron-rich triarylphosphine
decreased the catalytic activity of the rhodium complex and cyclopentadiene 2a was obtained in lower
yield at higher reaction temperature (entry 4). Bidentate ligand was inappropriate for the present reaction
and it took longer reaction time at higher temperature to consume cyclopropene-yne 1a (entry 5). Cationic
rhodium complex shortened the reaction time but the yield did not increase (entry 6). When RhCl(PPh3)3
was used, the best yield of 74% was achieved in short reaction time (entry 7). Halogenated nor ether type
solvent did not improve the yield (entries 8 and 9). The reaction proceeded even at room temperature but
the substrate was not completely consumed after 3 days (entry 10). At the elevated temperature, it was
promptly consumed but the yield was drastically diminished along with the formation of many
unidentified products (entry 11).

HETEROCYCLES, Vol. 76, No. 2, 2008
1263
Table 1. Screening of various reaction conditions
Ph
complex + ligand
(10 mol%)
Ph
Me
Me
Me
Me
O
O
toluene
1a
2a
Entry
1
Complex
Ligand
none
Temp./°C
reflux
60
Time/h
Yield/%
C.M.a
36
1/2[RhCl(cod)]2
1/2[RhCl(cod)]2
3
3
2
2PPh3
3
1/2[RhCl(cod)]2 2P(p-FC6H4)3
60
2
34
4
1/2[RhCl(cod)]2 2P(p-MeOC6H4)3 60-100
9
19
5
1/2[RhCl(cod)]2
[Rh(cod)2]BF4
DPPPb
80
60
10
1
22
6c
2PPh3
28
7
RhCl(PPh3)3
60
2
74
8c
9d
10
RhCl(PPh3)3
RhCl(PPh3)3
RhCl(PPh3)3
60
2
60
60
2
62
rt
72
29
11
RhCl(PPh3)3
reflux
0.25
33
a
b
c
Complex mixture. 1,2-Bis(diphenylphosphino)propane. 1,2-Dichloroethane
was used as a solvent. d 1,4-Dioxane was used as a solvent.
Other cyclopropene-ynes were submitted to the reaction in toluene using RhCl(PPh3)3 as a catalyst (Table
2). Cyclopropene-yne 1b with alkyl substituent at its alkyne terminus was also transformed into the corre-
Table 2. Intramolecular cycloaddition of various cyclopropene-ynes
R
RhCl(PPh3)3
(10 mol%)
R
Me
Me
Me
Z
Z
Me
toluene, 60 °C
1b-f
2b-f
Entry
R
Z
Time/h
Yield/%
60 (2b)
69 (2c)
64 (2d)
85 (2e)
69 (2f)
1
Ph(CH2)3
Ph
O
1b
1c
1d
6
4
2
NTs
NTs
3a
Me
2
4
Ph
C(CO2Et)2 1e
9
5a
Ph(CH2)3 C(CO2Et)2 1f
24
a The reaction was examined under reflux condition.

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HETEROCYCLES, Vol. 76, No. 2, 2008
sponding product 2b (entry 1). Nitrogen-tethered cyclopropene-ynes 1c and 1d were also appropriate
substrates and intramolecular reaction proceeded in acceptable yields (entries 2 and 3). Carbon-tethered
cyclopropene-ynes required longer reaction time than the corresponding heteroatom-tethered ones but
good yield was achieved (entries 4 and 5).
Introduction of alkyl substituent at the α-position of cyclopropenyl group significantly diminished the
formation of unidentified products and the corresponding bicyclic diene 2g was obtained in the best yield
of 90% (Table 3, entry 1). Even the bulky tert-butyl group at the alkyne terminus did not deter the
intramolecular reaction and comparable yield was achieved (entry 2). Also in the reaction of
cyclopropene-yne 1i with a methyl group at 2-position of cyclopropene ring, the desired product 2i was
provided in high yield after being stirred for prolonged reaction time (entry 3). On the contrary, in the
case of cyclopropene-yne 1j without methyl group at the 3-position, it was completely consumed within 2
h and the disappearance of cyclopropenyl moiety was ascertained by the NMR analyses of crude products
but expected cyclized product 2j was not detected (entry 4). These results imply that the methyl groups at
the 3-position are essential for the efficient cyclization.
Table 3. Intramolecular cycloaddition of α-substituted cyclopropene-ynes
R1
RhCl(PPh3)3
(10 mol%)
R1
R2
R2
O
O
R2
R3
R2
toluene, reflux
3
1
R3
2
Ph
1g-j
R1
2g-j
Ph
Entry
R2
Me
R3
H
Time/h
Yield/%
1a
2
Ph
1g
1h
1
2
8
2
90 (2g)
88 (2h)
90 (2i)
N.D.b
tert-Bu Me
H
3
Ph
Ph
Me Me 1i
Me 1j
4
H
a The reaction was examined at 60 °C. b Not detected.
The proposed reaction mechanism was depicted in Scheme 1. The coordination of alkynyl group realizes
selective approach of the metal center to C1-C3 single bond of the cyclopropene ring. The oxidative
addition of metal center along with the bond cleavage affords metallacyclobutene intermediate B. The
intramolecular alkyne insertion gives the bicyclic metallacyclohexadiene C and the following reductive
elimination regenerates the catalyst and the bicyclic cyclopentadiene is formed.

HETEROCYCLES, Vol. 76, No. 2, 2008
1265
R
R
Me
Me
Z
Z
I
Rh
R
R
I
III
Rh
Z
Rh
Z
1
3
2
A
C
R
III
Rh
Z
B
Scheme 1
The alkyne coordination to the metal center would be critical for the bond cleavage of cyclopropene.
Actually, the bond cleavage of cyclopropene 3 was not observed at all even in the presence of a
stoichiometric amount of RhCl(PPh3)3 at 80 °C (eq. 1).
Me Me
RhCl(PPh3)3
(1 equiv.)
(eq. 1)
no reaction
Ph
C6D6, rt-80 °C
OTBS
3
When cyclopropene 3 was submitted to the reaction with hex-3-yne, it was completely consumed at 80 °C
but no cross-coupled products were detected (eq. 2). These results imply that intramolecular coordination
of alkyne to metal center would be important for effective insertion to metallacyclobutene.
RhCl(PPh3)3
(10 mol%)
Et
Et
+
(eq. 2)
complex mixture
3
toluene, 80 °C
In conclusion, we developed Rh-catalyzed cycloaddition of various cyclopropene-ynes. The reaction was
initiated by carbon-carbon bond cleavage of cyclopropene ring and gave bicyclic cyclopentadienes. The

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HETEROCYCLES, Vol. 76, No. 2, 2008
alkyne coordination would facilitate the bond cleavage and intramolecular insertion realized the present
transformation.
EXPERIMENTAL
Anhydrous toluene, 1,2-dichloroethane, and 1,4-dioxane are commercially available. They were dried
over molecular sieves 4A (MS 4A) and degassed by argon bubbling before use. All reactions were
examined under an argon atmosphere. IR spectra were recorded with Horiba FT730 spectrophotometer.
NMR spectra were measured with JEOL AL-400 and Lambda500 spectrometers using tetramethylsilane
as an internal standard and CDCl3 as a solvent. Mass spectra were measured with JEOL JMS-SX102A
and elemental analyses with Perkin Elmer PE2400II.
Typical experimental procedure (Table 1, entry 7): RhCl(PPh3)3 (9.3 mg, 0.0101 mmol) was placed in
a flask and a toluene solution (2 mL) of cyclopropene-yne 1a (21.7 mg, 0.102 mmol) was added. The
reaction mixture was stirred at 60 °C for 2 h. The solvent was removed under reduced pressure and the
resulting crude products were purified by thin-layer chromatography to give pure bicyclic
cyclopentadiene 2a (16.0 mg, 0.0754 mmol, 74% yield).
(3,3-Dimethylcycloprop-1-enyl)methyl 3-phenylprop-2-ynyl ether (1a). Colorless oil; IR (neat) 1757,
1
1092, 692 cm-1; H-NMR δ 1.20 (s, 6H), 4.47 (s, 2H), 4.65 (d, J= 1.6 Hz, 2H), 7.15 (brs, 1H), 7.31-7.32
13
(m, 3H), 7.44-7.47 (m, 2H); C-NMR δ 20.0, 27.3, 58.0, 64.2, 84.6, 86.5, 116.1, 122.5, 128.2, 128.4,
131.2, 131.7; HRMS (EI+) for M found m/z 212.1208, calcd for C15H16O: 212.1201.
(3,3-Dimethylcycloprop-1-enyl)methyl 6-phenylhex-2-ynyl ether (1b). Colorless oil; IR (neat) 1757,
1
1088, 700 cm-1; H-NMR δ 1.18 (s, 6H), 1.81-1.88 (m, 2H), 2.23-2.26 (m, 2H), 2.72 (t, J= 7.6 Hz, 2H),
4.23 (t, J= 1.8 Hz, 2H), 4.57 (d, J= 1.2 Hz, 2H), 7.11 (brs, 1H), 7.17-7.19 (m, 3H), 7.26-7.30 (m, 2H);
13C-NMR δ 18.3, 19.9, 27.3, 30.2, 34.8, 57.8, 63.9, 76.1, 86.8, 115.9, 125.8, 128.3, 128.4, 131.4, 141.4;
HRMS (FAB+) for M found m/z 254.1651, calcd for C18H22O: 254.1671.
N-[(3,3-Dimethylcycloprop-1-enyl)methyl]-N-(3-phenylprop-2-ynyl)-4-methylphenylsulfonylamide
(1c). White solid; mp 79 °C; IR (CH2Cl2) 1757, 1163, 814, 692 cm-1; 1H-NMR δ 1.13 (s, 6H), 2.35 (s, 3H),
4.39 (s, 2H), 4.42 (d, J= 0.8 Hz, 2H), 6.98 (brs, 1H), 7.09-7.12 (m, 2H), 7.22-7.28 (m, 5H), 7.77 (d, J=
8.4 Hz, 2H); 13C-NMR δ 20.1, 21.5, 27.1, 37.3, 42.9, 81.5, 85.8, 117.3, 122.1, 127.8, 128.1, 128.4, 129.4,
129.5, 131.5, 135.7, 143.5; HRMS (FAB+) for M+1 found m/z 366.1544, calcd for C22H24NO2S:
366.1527.
N-But-2-ynyl-N-[(3,3-Dimethylcycloprop-1-enyl)methyl]-4-methylphenylsulfonylamide (1d). Yellow
oil; IR (neat) 1757, 1163, 816 cm-1; 1H-NMR δ 1.09 (s, 6H), 1.59 (t, J= 2.5 Hz, 3H), 2.42 (s, 3H), 4.09 (d,
13
J= 2.5 Hz, 2H), 4.35 (s, 2H), 6.88 (s, 1H), 7.29 (d, J= 8.4 Hz, 2H), 7.73 (d, J= 8.4 Hz, 2H); C-NMR δ

HETEROCYCLES, Vol. 76, No. 2, 2008
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3.3, 20.0, 21.5, 27.0, 36.9, 42.6, 71.6, 81.7, 117.0, 127.8, 129.2, 129.5, 136.1, 143.2; HRMS (FAB+) for
M+1 found m/z 304.1371, calcd for C17H22NO2S: 304.1371.
Diethyl 5-(3,3-Dimethylcycloprop-1-enyl)-1-phenylpent-1-yne-4,4-dicarboxylate (1e). Colorless oil;
IR (neat) 1739, 692 cm-1; 1H-NMR δ 1.10 (s, 6H), 1.26 (t, J= 7.2 Hz, 6H), 3.13 (s, 2H), 3.30 (d, J= 0.8 Hz,
13
2H), 4.19-4.26 (m, 4H), 6.95 (brs, 1H), 7.27-7.28 (m, 3H), 7.34-7.37 (m, 2H); C-NMR δ 14.2, 18.3,
23.8, 27.4, 28.9, 56.2, 61.8, 83.4, 84.3, 116.0, 123.1, 127.8, 128.0, 130.0, 131.5, 169.3; HRMS (FAB+) for
M found m/z 354.1823, calcd for C22H26O4: 354.1831.
Diethyl 8-(3,3-dimethylcycloprop-1-enyl)-1-phenyloct-4-yne-7,7-dicarboxylate (1f). Colorless oil; IR
(neat) 1738, 700 cm-1; 1H-NMR δ 1.09 (s, 6H), 1.26 (t, J= 7.2 Hz, 6H), 1.72-1.79 (m, 2H), 2.11-2.16 (m,
2H), 2.68 (t, J= 7.6 Hz, 2H), 2.90 (t, J= 2.2 Hz, 2H), 3.25 (d, J= 1.2 Hz, 2H), 4.17-4.22 (m, 4H), 6.92 (brs,
1H), 7.18-7.20 (m, 3H), 7.28-7.30 (m, 2H); 13C-NMR δ 14.2, 18.2, 18.3, 23.2, 27.4, 28.7, 30.6, 34.7, 56.2,
61.6, 74.9, 83.0, 115.9, 125.7, 128.2, 128.4, 130.1, 141.6, 169.5; HRMS (FAB+) for M found m/z
396.2323, calcd for C25H32O4: 396.2301.
1-(3,3-Dimethylcycloprop-1-enyl)-3-phenylpropyl 3-phenylprop-2-ynyl ether (1g). Yellow oil; IR
(neat) 1749, 1085, 694 cm-1; 1H-NMR δ 1.21 (s, 3H), 1.24 (s, 3H), 1.96-2.11 (m, 2H), 2.74-2.88 (m, 2H),
4.37 (d, J= 15.6 Hz, 1H), 4.53 (d, J= 15.6 Hz, 1H), 4.66 (dd, J= 6.4, 6.4 Hz, 1H), 7.14 (s, 1H), 7.17-7.44
13
(m, 10H); C-NMR δ 20.1, 27.8, 27.9, 31.6, 35.9, 56.8, 73.6, 85.3, 86.0, 116.5, 122.6, 125.7, 128.2,
128.3, 128.3, 128.5, 131.7, 133.7, 141.7; HRMS (FAB+) for M found m/z 316.1841, calcd for C23H24O:
316.1827.
1-(3,3-Dimethylcycloprop-1-enyl)-3-phenylpropyl 4,4-dimethylpent-2-ynyl ether (1h). Colorless oil;
1
IR (neat) 1749, 1095, 700 cm-1; H-NMR δ 1.19 (s, 6H), 1.21 (s, 9H), 1.94-2.05 (m, 2H), 2.70-2.85 (m,
2H), 4.13 (d, J= 15.4 Hz, 1H), 4.29 (d, J= 15.4 Hz, 1H), 4.57 (dd, J= 6.2, 6.2 Hz, 1H), 7.09 (s, 1H),
7.17-7.23 (m, 3H), 7.27-7.31 (m, 2H); 13C-NMR δ 19.9, 27.5, 27.8, 27.9, 31.0, 31.8, 35.9, 56.6, 73.1, 74.4,
95.1, 116.1, 125.7, 128.3, 128.4, 133.8, 141.9; HRMS (FAB+) for M found m/z 296.2153, calcd for
C21H28O: 296.2140.
3-Phenylprop-2-ynyl 3-phenyl-1-(2,3,3-trimethylcycloprop-1-enyl)propyl ether (1i). Yellow oil; IR
1
(neat) 1851, 1088, 694 cm-1; H-NMR δ 1.15 (s, 3H), 1.16 (s, 3H), 1.94-2.10 (m, 2H), 2.05 (s, 3H),
2.74-2.85 (m, 2H), 4.32 (d, J= 15.6 Hz, 1H), 4.50 (d, J= 15.6 Hz, 1H), 4.59 (dd, J= 6.4, 6.4 Hz, 1H),
7.17-7.32 (m, 8H), 7.42-7.44 (m, 2H); 13C-NMR δ 9.2, 21.0, 26.0, 26.1, 31.8, 36.2, 56.7, 73.4, 85.6, 85.9,
122.4, 122.7, 124.1, 125.7, 128.2, 128.3, 128.5, 131.7, 142.0; HRMS (FAB+) for M found m/z 330.1990,
calcd for C24H26O: 330.1984.
3,3-Dimethyl-2-phenyl-7-oxabicyclo[3.3.0]octa-1,4-diene (2a). White solid; mp 94 °C; IR (CH2Cl2)
1595, 1462, 1028, 768, 698 cm-1; 1H-NMR δ 1.43 (s, 6H), 4.55 (d, J= 2.0 Hz, 2H), 4.78 (s, 2H), 5.85 (brs,

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HETEROCYCLES, Vol. 76, No. 2, 2008
1H), 7.19-7.39 (m, 5H); 13C-NMR δ 23.2, 62.4, 65.4, 67.1, 125.9, 126.7, 128.4, 133.4, 134.8, 140.1, 144.4,
145.0; HRMS (FAB+) for M found m/z 212.1215, calcd for C15H16O: 212.1201.
3,3-Dimethyl-2-(3-phenylpropyl)-7-oxabicyclo[3.3.0]octa-1,4-diene (2b). Colorless oil; IR (neat) 1603,
1456, 1014, 746, 700 cm-1; 1H-NMR δ 1.12 (s, 6H), 1.80-1.85 (m, 2H), 2.12-2.14 (m, 2H), 2.65 (t, J= 7.5
Hz, 2H), 4.43 (s, 2H), 4.49 (s, 2H), 5.66 (s, 1H), 7.18-7.21 (m, 3H), 7.26-7.30 (m, 2H); 13C-NMR δ 22.3,
25.5, 29.3, 36.1, 62.5, 65.3, 65.6, 125.7, 128.3, 128.3, 128.9, 139.6, 142.0, 142.9, 145.8; HRMS (FAB+)
for M-1 found m/z 253.1591, calcd for C19H21O: 253.1593.
3,3-Dimethyl-7-[(4-methylphenyl)sulfonyl]-2-phenyl-7-azabicyclo[3.3.0]octa-1,4-diene (2c). White
1
solid; mp 125 °C; IR (CH2Cl2) 1597, 1460, 1165, 814, 762, 696 cm-1; H-NMR δ 1.32 (s, 6H), 2.42 (s,
3H), 4.10 (d, J= 1.6 Hz, 2H), 4.32 (s, 2H), 5.85 (brs, 1H), 7.23-7.39 (m, 7H), 7.77 (d, J= 8.4 Hz, 2H);
13C-NMR δ 21.6, 22.8, 46.6, 48.4, 60.8, 126.5, 126.8, 127.5, 128.5, 129.7, 133.9, 134.5, 135.8, 139.0,
140.5, 142.8, 143.5; HRMS (FAB+) for M+1 found m/z 366.1528, calcd for C22H24NO2S: 366.1527.
3,3-Dimethyl-2-methyl-7-[(4-methylphenyl)sulfonyl]-7-azabicyclo[3.3.0]octa-1,4-diene (2d). White
solid; mp 75 °C; IR (CH2Cl2) 1596, 1458, 1165, 817, 785 cm-1; 1H-NMR δ 1.02 (s, 6H), 1.66 (s, 3H), 2.42
(s, 3H), 3.96 (s, 2H), 4.01 (d, J= 2.0 Hz, 2H), 5.70 (brs, 1H), 7.32 (d, J= 7.8 Hz, 2H), 7.74 (d, J= 7.8 Hz,
2H); 13C-NMR δ 10.4, 21.6, 21.8, 46.1, 47.1, 60.4, 127.5, 129.6, 131.7, 133.9, 135.4, 140.7, 141.4, 143.3;
HRMS (FAB+) for M+1 found m/z 304.1371, calcd for C17H22NO2S: 304.1371.
Diethyl 7,7-dimethyl-6-phenylbicyclo[3.3.0]octa-5,8-diene-3,3-dicarboxylate (2e). Yellow oil; IR
1
(neat) 1732, 1597, 1462, 796, 762 cm-1; H-NMR δ 1.25 (t, J= 7.2 Hz, 6H), 1.34 (s, 6H), 3.05 (d, J= 2.0
Hz, 2H), 3.29 (s, 2H), 4.17-4.23 (m, 4H), 5.83 (brs, 1H), 7.18-7.22 (m, 1H), 7.26-7.38 (m, 2H), 7.41-7.44
13
(m, 2H); C-NMR δ 14.2, 23.4, 33.3, 35.4, 60.2, 61.7, 65.1, 125.7, 126.9, 128.1, 135.8, 135.9, 142.3,
143.3, 144.2, 171.2; HRMS (FAB+) for M found m/z 354.1829, calcd for C22H26O4: 354.1831.
Diethyl 7,7-dimethyl-6-(3-phenylpropyl)bicyclo[3.3.0]octa-5,8-diene-3,3-dicarboxylate (2f). Colorless
1
oil; IR (neat) 1734, 1458, 746, 700 cm-1; H-NMR δ 1.05 (s, 6H), 1.23 (t, J= 7.2 Hz, 6H), 1.86-1.94 (m,
2H), 2.13-2.16 (m, 2H), 2.64 (t, J= 7.8 Hz, 2H), 2.96 (d, J= 1.6 Hz, 2H), 3.00 (s, 2H), 4.15-4.21 (m, 4H),
5.64 (brs, 1H), 7.16-7.21 (m, 3H), 7.28-7.30 (m, 2H); 13C-NMR δ 14.2, 22.7, 25.8, 29.7, 33.4, 33.6, 36.3,
60.2, 61.5, 65.1, 125.5, 128.1, 128.3, 131.7, 138.6, 142.3, 144.5, 144.6, 171.3; HRMS (FAB+) for M-1
found m/z 395.2232, calcd for C25H31O4: 395.2223.
3,3-Dimethyl-2-phenyl-6-(2-phenylethyl)-7-oxabicyclo[3.3.0]octa-1,4-diene (2g). Yellow oil; IR (neat)
1601, 1456, 1028, 766, 694 cm-1; 1H-NMR δ 1.42 (s, 3H), 1.44 (s, 3H), 1.99-2.05 (m, 2H), 2.77-2.81 (m,
2H), 4.71 (ddd, J= 1.7, 6.1, 6.1 Hz, 1H), 4.79 (d, J= 14.2 Hz, 1H), 4.86 (d, J= 14.2 Hz, 1H), 5.85 (d, J=
13
1.7 Hz, 1H), 7.17-7.31 (m, 8H), 7.36-7.40 (m, 2H); C-NMR δ 23.0, 23.4, 31.5, 37.1, 62.0, 66.7, 75.3,
125.7, 125.9, 126.7, 128.3, 128.4, 128.5, 133.9, 134.8, 140.1, 141.8, 144.7, 148.3; HRMS (FAB+) for M
found m/z 316.1801, calcd for C23H24O: 316.1827.

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2-tert-Butyl-3,3-dimethyl-6-(2-phenylethyl)-7-oxabicyclo[3.3.0]octa-1,4-diene (2h). Colorless oil; IR
1
(neat) 1603, 1456, 1030, 748, 700 cm-1; H-NMR δ 1.18 (s, 9H), 1.70 (s, 6H), 1.91-1.96 (m, 2H),
2.72-2.77 (m, 2H), 4.51-4.55 (m, 2H), 4.61 (d, J= 13.2 Hz, 1H), 5.46 (d, J= 1.2 Hz, 1H), 7.16-7.22 (m,
13
3H), 7.28-7.30 (m, 2H); C-NMR δ 23.2, 23.6, 30.8, 31.6, 34.8, 37.1, 63.4, 66.3, 74.7, 125.6, 128.2,
128.4, 131.3, 140.8, 142.0, 147.1, 149.8; HRMS (FAB+) for M found m/z 296.2159, calcd for C21H28O:
296.2140.
2-Phenyl-6-(2-phenylethyl)-3,3,4-trimethyl-7-oxabicyclo[3.3.0]octa-1,4-diene (2i). Yellow oil; IR
(neat) 1597, 1456, 1030, 746, 694 cm-1; 1H-NMR δ 1.30 (s, 3H), 1.32 (s, 3H), 1.84 (s, 3H), 1.92-2.04 (m,
1H), 2.07-2.17 (m, 1H), 2.70-2.82 (m, 2H), 4.78-4.88 (m, 3H), 7.16-7.30 (m, 8H), 7.34-7.38 (m, 2H);
13C-NMR δ 10.3, 22.6, 23.1, 31.4, 36.7, 62.3, 66.9, 75.2, 125.4, 125.7, 126.2, 128.3, 128.4, 128.4, 135.3,
138.6, 140.9, 142.2, 142.7, 144.9; HRMS (FAB+) for M found m/z 330.1981, calcd for C24H26O:
330.1984.
1-(tert-Butyldimethylsiloxy)-1-(3,3-dimethylcyclopropene-1-yl)-3-phenylpropane (3). Colorless oil.
IR (neat) 1757, 1458, 1254, 1095, 837, 775, 698 cm-1, 1H-NMR δ 0.07 (s, 3H), 0.07 (s, 3H), 0.92 (s, 9H),
1.18 (s, 3H), 1.19 (s, 3H), 1.86-2.02 (m, 2H), 2.64-2.81 (m, 2H), 4.71 (t, J= 6.0 Hz, 1H), 6.95 (s, 1H),
13
7.17-7.21 (m, 3H), 7.25-7.32 (m, 2H); C-NMR δ -5.09, -4.47, 18.3, 20.9, 25.8, 27.6, 27.9, 31.8, 38.6,
69.1, 114.0, 125.8, 128.4, 128.4, 136.9, 142.3; HRMS (EI+) for M found m/z 316.2186, calcd for
C20H32OSi: 316.2222.
ACKNOWLEDGEMENTS
This research was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
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