cyclopentene (prepared, 1 equiv.),
tetrahydrofuran (distilled from sodium-benzophenone ketyl, 5 mL/mmol),
LHMDS (Aldrich, 1 M solution in THF, 2.5 equiv.),
acetaldehyde (Lancaster, extremely volatile, 1.1 equiv.),
saturated ammonium chloride solution (5 mL/mmol),
diethyl ether (GPR, 2 x 10 mL/mmol),
water (10 mL/mmol),
ethyl acetate (GPR, 10 mL/mmol)

A solution of the cyclopentenol (344 mg, 1.22 mmol, 1 equiv.), in distilled tetrahydrofuran (6 mL), was cooled to -78 ºC and lithium hexamethyldisilazane (LHMDS) (3.1 mL of a 1 M solution in tetrahydrofuran, 3.05 mmol, 2.5 equiv.) was added. The mixture was allowed to stir for 2 hours keeping the temperature constant at -78 ºC; acetaldehyde (0.084 mL, 59 mg, 1.34 mmol, 1.1 equiv.) was then added. The reaction mixture was allowed to warm to 0 ºC over 2 hours, after which the reaction was quenched with saturated ammonium chloride solution (6 mL). Extraction with diethyl ether (2 x 12 mL) was followed by washing of the organics with water (12 mL) and re-extraction of the combined aqueous layers with ethyl acetate (12 mL/mmol). The combined organic fractions were dried over magnesium sulfate and the solvent reduced in vacuo. The crude oil was purified by flash column chromatography (petroleum ether/diethyl ether, 10 : 1 to 5 : 1) to yield the product as a pale yellow solid (185 mg, 46 % (92 % based on recovered sm)). Also obtained was starting material (172 mg, 50 %).

¹ H NMR (300 MHz; CDCl₃) 5.90 (1 H, dd, J 6.0 and 1.0, CH), 5.69 (1 H, dd, J 6.0 and 1.0, CH), 5.47 (1 H, q, J 6.5, CCHO), 4.16 (1 H, dt, J 5.5 and 1.0, CHO), 3.91 (1 H, d, J 5.5, CHO), 3.40 (1 H, s, OH [exch]), 3.08 (1 H, s, OH [exch]), 2.56 (1 H, dd, J 17.0 and 2.0, HCH), 2.19 (1 H, dd, J 17.0 and 2.0, HCH), 1.39 (3 H, d, J 6.5, CH₃), 1.18 (9 H, s, (CH₃)₃C), 0.15 (9 H, s, (CH₃)₃Si)

S. Caddick, S. Khan, N. J. Smith, D. M. Barr, V. M. Delisser, Tetrahedron Lett., 1997, 38, 5053