HETEROCYCLES, Vol. 80, No. 2, 2010
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Synthesis of oxabicyclic compound 9a: 9-Oxa-1-Phenyl-8-vinylbicyclo[4.2.1]nonane
In a 250 mL round bottom flask, ketoaldehyde 8a (126 mg, 0.66 mmol, 1.05 equiv) and reagent 1 (193
_
o
mg, 0.63 mmol, 1.00 equiv) in 150 mL of CH2Cl2 were mixed and cooled to 78 C and stirred for 30
minutes. Next, BF3·Et2O (0.13 mL, 1.00 mmol, 1.50 equiv) was added to the flask and stirred for 12 h at
o
o
_78 C, followed by 9 h at 0 C (different bath). The reaction mixture was quenched with sat. aqueous
NaHCO3 (20 mL) and extracted with Et2O (4 x 25 mL). The combined organic layers were dried over
anhydrous Na2SO4, filtered and the solvent was removed by rotary evaporator. Flash chromatography
(0_5% EtOAc in hexanes) provided a clear oil (85.0 mg, 60.0% yield). TLC (25% EtOAc in hexanes,
1
magic stain): Rf 0.69; H NMR (CDCl3, 300 MHz): ꢀ 7.48 (dd, J = 1.4, 8.5 Hz, 2H), 7.31 (m, 3H), 5.99
(ddd, J = 7.3, 10.2, 17.5 Hz, 1H), 5.15 (ddd, J = 1.0, 1.9, 10.3 Hz, 1H), 5.00 (ddd, 1.2, 1.9, 17.0 Hz, 1H),
4.70 (m, 1H), 3.02 (dt, J = 5.1, 8.2 Hz, 1H), 2.71 (q, J = 9.9 Hz, 1H), 2.44 (td, J = 9.4, 12.9 Hz, 1H), 2.10
13
(m, 3H), 1.72 (m, 5H); C NMR (CDCl3, 100 MHz): ꢀ 148.4, 136.7, 128.1, 126.1, 124.9, 117.7, 87.0,
1
76.6, 56.1, 44.5, 38.4, 34.7, 25.1, 24.9; IR (CDCl3, cast film): cm– 3077, 3026, 2927, 2859, 1638, 1602,
1492, 1470, 1446, 1350, 1095, 1072, 1013, 914, 753, 700; HRMS (EI, m/z) calculated for C16H20O:
228.1514, found: 228.1515 [M+]. HPLC: Chiralcel OD (0.46 cm i.d. X 25 cm), 5% i-PrOH/hexanes,
0.50 mL/min., UV detection at 210 nm, major peak at 7.1 min., minor peak at 8.5 min., 93% ee. A small
quantity of 11a, 5-[5-(5-Oxo-5-phenyl-pentyl)-3-vinyl-tetrahydro-furan-2-yl]-1-phenyl-pentan-1one, was
also isolated. Flash chromatography (0_5% EtOAc in hexanes) yielded a white gel (28 mg, 10 % yield).
1
TLC (25% EtOAc in hexanes, magic stain): Rf 0.39; H NMR (CDCl3, 400 MHz): ꢀ 7.95 (m, 4H), 7.55
(m, 2H), 7.46 (m, 4H), 5.74 (ddd, J = 9.0, 9.3, 18.0 Hz, 1H), 5.00 (d, J = 5.2 Hz, 1H), 4.97 (s, 1H), 3.79
(m, 2H), 2.97 (q, J = 8.4 Hz, 4H), 2.81 (m, 1H), 2.19 (ddd, J = 6.8, 8.0, 15.8 Hz, 1H), 1.76 (m, 5H), 1.46
(m, 8H); 13C NMR (CDCl3, 100 MHz): ꢀ 200.3, 138.7, 137.1, 132.8, 128.5, 128.0, 115.0, 81.3, 78.4, 46.7,
1
38.5, 38.3, 36.2, 31.6, 26.2, 24.5; IR (CDCl3, cast film): cm– 3066, 2936, 2862, 1686, 1598, 1449, 1224,
1002, 752, 691; HRMS (ES, m/z) calculated for C28H34O3Na: 441.2400, found: 441.2402 [(M+Na)+].
[ꢁ]25D 16.61 (c = 0.92, CHCl3).
ACKNOWLEDGMENTS
The authors are grateful to the Natural Sciences and Engineering Research Council (NSERC) of Canada
for financial support of this research.
REFERENCES
1. a) M. C. Elliott, J. Chem. Soc., Perkin Trans. 1, 2002, 2301; b) J. P. Wolfe and M. B. Hay,
Tetrahedron, 2007, 63, 261.
2. F. Peng and D. G. Hall, J. Am. Chem. Soc., 2007, 129, 3070.