SCHEME 4
2.95 (4H, s), 2.25 (1H, dd, J ) 14.0, 6.1 Hz), 2.08 (1H, dd, J )
14.0, 8.0 Hz), 1.64 (1H, m), 1.39 (1H, apparent septet, J ) 6.5
Hz), 1.29 (1H, m), 1.17 (2H, m), 1.04 (3H, m), 0.75 (3H, d, J )
6.5 Hz), 0.72 (6H, d, J ) 6.5 Hz); 13C NMR (TFA): δ 210.0,
123.6, 40.9, 38.8, 33.8, 32.0, 29.7, 29.5, 26.3, 23.2, 23.1, 19.9.
2-Cyclohexylcyclopentane-1,3-dione (6d): Solid. mp: 216-
218 °C (from EtOAc); 1H NMR (TFA): δ 2.94 (4H, s), 2.53 (1H,
m), 1.74-1.50 (6H, m), 1.22 (4H, m); 13C NMR (TFA): δ 209.7,
128.2, 35.3, 32.1, 30.9, 27.9, 27.1.
2-Phenylcyclopentane-1,3-dione (6e): Colorless solid. mp:
1
233-234 °C (dec) (from EtOAc), lit.1b 231-232 °C; H NMR
(TFA): δ 7.28 (5H, m), 2.98 (4H, s); 13C NMR (TFA): δ 207.5,
131.4, 130.8, 130.6, 127.4, 122.7, 31.8.
2-(2-Phenyl-1-ethenyl)cyclopentane-1,3-dione (6f): Colorless
1
solid. mp: 209-210 °C (from EtOH); H NMR (TFA): δ 7.34-
7.15 (6H), 6.64 (1H, d, J ) 16.7 Hz), 2.99 (4H, s); 13C NMR
(TFA): δ 208.0, 138.4, 138.2, 131.0, 130.9, 128.6, 120.1, 112.4,
32.2.
(cis)-8-Methylbicyclo[4.3.0]nonane-7,9-dione (8a): Colorless
solid. mp: 151-151.5 °C (from EtOAc), lit.15 149-151 °C; IR
1
(Nujol): 1699 cm-1; H NMR (TFA): δ 3.06 (2H, m), 2.04 (2H,
m), 1.75 (3H, s), 1.66-1.28 (6H, m); 13C NMR (TFA): δ 212.5,
118.3, 44.5, 25.0, 20.4, 5.5; MS m/z: 166 (M+).
(cis)-8-Nonylbicyclo[4.3.0]nonane-7,9-dione (8b): Colorless
liquid. IR (film): 1709 cm-1; 1H NMR (CDCl3): δ 2.81 (2H, broad
m), 2.60-0.85 (m); 13C NMR (CDCl3): δ 202.7, 117.8, 41.9, 32.1,
29.8, 29.7, 29.5, 29.5, 28.3, 23.4, 22.8, 22.8, 19.6, 14.2; MS m/z:
278 (M+).
SCHEME 5
(cis)-8-(2,6-Dimethylheptyl)bicyclo[4.3.0]nonane-7,9-dione (8c):
Colorless solid. mp: 111-112 °C (from hexane); IR (Nujol): 1708
1
cm-1; H NMR (CDCl3): δ 2.73 (2H, m), 2.15 (1H, dd, J ) 6.8,
3.0 Hz), 2.01 (1H, dd, J ) 6.8, 4.0 Hz), 1.88 (2H, m), 1.70 (3H,
m), 1.48 (1H, m), 1.45 (4H, narrow m), 1.36-1.19 (3H, m), 1.15-
1.05 (3H, m), 0.85 (6H, d, J ) 7.0 Hz), 0.82 (3H, d, J ) 6.5 Hz);
13C NMR (CDCl3): δ 200.4, 116.2, 41.9, 39.6, 37.4, 32.5, 28.8,
28.2, 25.1, 23.8, 23.0, 22.8, 20.2, 19.7.
1,3-diones, which NMR revealed are largely enolized, in very
good yields. The geminally disubstituted cyclobutene 12 and
the cyclopentene 16 followed different reaction pathways to give
cyclopentane-1,2-diones, also mainly enolized, in modest yields.
(cis)-8-Cyclohexylbicyclo[4.3.0]nonane-7,9-dione (8d): Color-
less solid. mp: 210-212 °C (from EtOAc); IR (Nujol): 1704 cm-1
;
Experimental Section
1H NMR (TFA): δ 3.08 (2H, m), 2.48 (1H, m), 2.01-1.86 (2H,
m), 1.73-1.08 (16H); 13C NMR (TFA): δ 212.3, 127.3, 44.5, 35.1,
31.1, 27.9, 27.1, 25.0, 20.0.
General Procedure: 2-Methylcyclopentane-1,3-dione (6a). A
solution of acetaldehyde diethyl acetal 4a (0.118 g, 1.00 mmol) in
dry CH2Cl2 (20 mL) was cooled in a dry ice/acetone bath under
N2. Freshly distilled BF3 etherate (0.25 mL, 2.0 mmol) was added,
followed by a solution of 1 (0.34 g, 1.5 mmol) in dry CH2Cl2 (5.0
mL) over 10 min. The mixture was stirred overnight by which time
the mixture had attained rt. Saturated aqueous NaHCO3 was added,
and the aqueous layer was re-extracted with ether. The combined
organic solutions were washed with brine, dried over anhydrous
Na2SO4, and concentrated under reduced pressure to give 5a as an
oily residue. For the crude 5a: 13C NMR (CDCl3): δ 212.2, 210.1,
93.52, 93.47, 76.1, 76.0, 65.3, 65.0, 41.6, 40.9, 24.1, 23.7, 15.5
(2C), 14.1 (2C). The mixture 5a, without further purification, was
dissolved in TFA (2.0 mL), and Amberlyst 15 (0.1 g) was added.
The solution was heated under reflux for 10 h. After cooling, the
solution was diluted with Et2O (20 mL). Activated charcoal was
added, and the suspension was stirred for 30 min at reflux
temperature. The suspension was filtered through Celite and
evaporated under reduced pressure to provide 6a (0.088 g, 79%)
as a colorless solid; mp: 213-215 °C (from EtOH), lit.10 210-211
°C; 1H NMR (TFA): δ 2.57 (4H, s), 1.37 (3H, s); 13C NMR
(TFA): δ 209.5, 119.3, 31.8, 5.4.
(cis)-8-Phenylbicyclo[4.3.0]nonane-7,9-dione (8e): Colorless
solid. mp: 227-228 °C (from EtOAc), lit.16 229-230 °C; 1H NMR
(TFA): δ 7.30 (3H, m), 7.15 (2H, m), 3.18 (2H, m), 2.00 (2H, m),
1.75 (2H, m), 1.54 (4H, m); 13C NMR (TFA): δ 210.6, 132.2,
131.4, 131.2, 127.0, 122.2, 44.4, 25.2, 20.7.
(cis)-8-(2-Phenyl-1-ethenyl)bicyclo[4.3.0]nonane-7,9-dione (8f):
Colorless solid. mp: 207-209 °C (from EtOAc); 1H NMR
(TFA): δ 7.36-7.16 (6H), 6.63 (1H, d, J ) 16.8 Hz), 3.12 (2H,
m), 2.11-1.95 (2H, m), 1.76-1.52 (6H); 13C NMR (TFA): δ 210.0,
138.7, 138.3, 131.0, 130.8, 130.8, 128.6, 112.3, 44.5, 25.3, 20.6.
2-Ethyl-3,4,6,7-tetrahydro-2H-cyclopenta[b]pyran-5-one (11):
1
Colorless liquid. IR (film): 1732, 1694 cm-1; H NMR (CDCl3):
δ 4.07 (1H, m), 2.54 (2H, m), 2. 43 (2H, m), 2.28 (1H, m), 2.14
(1H, m), 1.94 (1H, m), 1.78 (1H, m), 1.68 (1H, m), 1.56 (1H, m),
1.04 (3H, t, J ) 7.5 Hz); 13C NMR (CDCl3): δ 205.0, 185.9, 114.8,
81.7, 33.1, 27.6, 26.8, 25.5, 16.2, 9.7; MS m/z: 166 (M+).
3,4,4-Trimethylcyclopentane-1,2-dione (15a): Colorless solid.
1
mp: 79-80 °C (from EtOAc); IR (Nujol): 1702, 1656 cm-1; H
NMR (CDCl3): δ 6.51 (1H, broad s), 2.31 (2H, s), 1.92 (3H, s),
1.19 (6H, s); 13C NMR (CDCl3): δ 202.0, 152.8, 147.5, 48.5, 37.6,
27.1, 9.3; MS m/z: 140 (M+).
2-Nonylcyclopentane-1,3-dione (6b): Colorless solid. mp: 132-
1
133 °C (from EtOAc); IR (Nujol): 1711 cm-1; H NMR (TFA):
δ 2.94 (4H, s), 2.26 (2H, t, J ) 7.5 Hz), 1.40 (2H, m), 1.22-1.16
(12H, m), 0.74 (3H, t, J ) 6.5 Hz); 13C NMR (TFA): δ 210.0,
124.4, 33.7, 32.1, 31.2, 31.1, 31.0, 30.9, 28.8, 24.3, 22.1, 14.6.
2-(2,6-Dimethylheptyl)cyclopentane-1,3-dione (6c): Pale yel-
(15) (a) Wang, K. C.; Yu, S. S.; Liao, L. Y. Taiwan Yaoxue Zazhi 1975,
27, 77-85. (b) Zhu, W. H.; Cao, Y. R. J. East China UniV. Sci. Technol.
1998, 24, 335-338.
(16) Gren, E. Y.; Vanags, G. Dokl. Akad. Nauk SSSR 1961, 139, 866-
869.
1
low solid. mp: 123-124 °C (from EtOAc); H NMR (TFA): δ
358 J. Org. Chem., Vol. 71, No. 1, 2006