(+/-)-(R)-3-Hydroxycyclohexenylethanone 22

A solution of (S)-2-butyl-CBS-oxazaborolidine (prepared according to literature procedure[1]) in toluene (0.75 ml, 0.2M, 0.15 mmol) was added to a solution of the ene-dione 11 (207 mg, 1.5 mmol) in toluene (7 ml) at -78degC. To this was added a solution of catecholborane in THF (2.3 ml, 1.0 M, 2.25 mmol) over 15 min and stirred at -78degC for 24 h. Water (~ 1 ml) was added and the mixture was allowed to warm to 20-25degC. This was washed with saturated potassium carbonate solution (3 x 7 ml). The combined aqueous layers were extracted with ethyl acetate (3 x 20 ml). The combined organic layers were washed with hydrochloric acid (1.0 N, 1 x 60 ml), brine (1 x 60 ml), dried (Na2SO4) and concentrated in vacuo. Chromatography (1:1 ethyl acetate, petrol) afforded the alcohol 22 (75 mg, 36%) as a colourless oil.

Proton nmr, IR, MS, HRMS, TLC and GC data was identical to that obtained for the product 22 from the ipc2BCl reduction below.

[alpha]D = +41deg (c=1.5, CHCl3); 75% e.e.

or

(+)-Diisopinocampheylchloroborane[2] (61 mg, 0.64 mmol) was weighed out in a glove bag under argon. To this was added THF (1 ml) and the mixture cooled to -78degC. A solution of the ene-dione 11 (88 mg, 0.64 mmol) in THF (~ 0.6 ml) was added and the mixture was stirred at -70degC for 6 days. Methanol (2 ml) was added, the mixture allowed to warm to 20-25degC and concentrated in vacuo. Chromatography (1:1 ethyl acetate, petrol) afforded the alcohol 22 (25 mg, 28%) as a colourless oil.

delta(H) 1.44-1.67 (2H, m), 1.68-1.87 (1H, m) and 1.87-2.10 (2H, m) (4CH2, 5CH2, OH); 2.14-2.24 (2H, m, 6CH2); 2.29 (3H, s, CH3); 4.32-4.47 (1H, m, 3CH); 6.73 (1H, br s, 2CH).

delta(C) 18.9, 22.8, 25.3, 31.2 (CH3, 4CH2, 5CH2, 6CH2); 66.2 (3CH); 140.4 (1C); 141.0 (2CH); 199.9 (C=O).

vmax (liquid film); 3418 (br, OH); 2939; 2864; 1668 (alpha,beta-unsaturated ketone); 1258; 1235; 1079 cm(-1).

m/z (C.I., NH3); 158 (M + NH4⁺); 141 (MH+); high resolution measured at 158.1182; C8H12O2 + NH4 requires 158.1181 (< 1 ppm error).

T.L.C.; Rf ~ 0.12 (1:1 ethyl acetate, petrol).

G.C. (50degC to 240degC at 10degC min(-1)); RT = 9.7 mins.

[alpha]D = +16deg (c=0.5, CHCl3); 29% e.e.