CHIRAL SYNTHESIS VIA ORGANOBORANES .42. SELECTIVE REDUCTIONS .57. EFFICIENT KINETIC RESOLUTION OF REPRESENTATIVE ALPHA-TERTIARY KETONES WITH B-CHLORODIISOPINOCAMPHEYLBORANE

Kinetic resolution of racemic alpha-tertiary ketones with 0.5-0.6 mola r equiv of B-chlorodiisopinocampheylborane provides the product alcoho ls in very high diastereomeric and enantiomeric excess, with the unrea cted ketone recovered in very high ee. For example, ethyl 1-methyl-8-o xocyclopentane- and -cyclohexanecarboxylates are partially reduced to recover the ketone in 91 greater than or equal to 99% ee and the produ ct alcohols in up to 94% de, with >90% ee for the major diastereomer. Bicyclic ketones, such as 1-methyl- and 1-ethylnorcamphor, camphor, an d camphenilone, are readily resolved to provide the ketone in 92 to gr eater than or equal to 99% ee, with the product alcohol recovered in h igh de and ee. ospiro[bicyclo[3.2.1]octane-2,2'(3'H)-furan]-3-one is r esolved to provide the ketone in greater than or equal to 99% ee and t he product alcohol in greater than or equal to 99% de. In all the case s studied, the R-isomer of the ketone is recovered when (d)Ipc(2)BCl i s used for kinetic resolution, while (l)Ipc(2)BCl provides the S-keton e. Optimum conditions for obtaining the product alcohol, or the ketone , or both, in very high yields and ee have been established.