9-Borabicyclo(3.3.1)nonane → (S)-3-cyclohexyl-1-propyn-3-ol

Participants

Reaction Conditions

Reaction Steps

A mixture of 1.6 liters 0.5M 9-borabicyclo[3.3.1]nonane in tetrahydrofuran and 122.6 g (-)-α-pinene, 99%+ pure, was heated at reflux under nitrogen for 4 hr., at which time the excess (-)-α-pinene and tetrahydrofuran were removed under vacuum to leave a thick oil. The contents of the flask were cooled to 0° C. and 80 g of 3-cyclohexylprop-1-yn-3-one, prepared according to Preparation 8, was added with stirring. The resulting mixture was allowed to warm to 23° C. and was stirred at that temperature for 16 hr. Excess S-Alpine borane was destroyed by adding 44 ml propionaldehyde and stirring at 23° C. for 1 hr. The liberated (-)-α-pinene was removed by vacuum distillation. The resulting mixture was diluted with 400 ml tetrahydrofuran followed by 300 ml 3N sodium hydroxide. To this stirred mixture was added in dropwise fashion 300 ml 30% hydrogen peroxide over 1 hr. The mixture was heated at 40° C. for 3 hr. After cooling, the mixture was extracted with diethyl ether and this extract was dried over magnesium sulfate. Evaporation of the solvent and purification of the residue by silica gel flash chromatography using 5% ethyl acetate-hexane gave 56 g of (S)-3-cyclohexyl prop-1-yn-3-ol, which by nmr analysis was shown to be 90% e.e. Recrystallization from hexane gave 45 g of the pure S isomer, mp 56°-58°, [α]D25 =-11.1° (C=0.53, Et2O)

Provenance & Evidence