Hydroboration. XVIII. The Reaction of Diisopinocampheylborane with Representative cis-Acyclic, Cyclic, and Bicyclic Olefins. A Convenient Synthesis of Optically Active Alcohols and Olefins of High Optical Purity and Established Configuration

Abstract

Optically active diisopinocampheylborane, readily synthesized by the hydroboration of optically active α-pinene, reacts readily with cis-2-butene to yield diisopinocampheyl-2-butylborane. Oxidation with alkaline hydrogen peroxide yields isopinocampheol and 2-butanol, the latter in optical purity of 87%. (+)-α-Pinene yields (-)-2-butanol ([α]d -11.8°); (-)-α-pinene yields (+)-2-butanol ([α]d +-11-7°). The reaction appears to be general for a number of cis-acyclic, cyclic, and bicyclic olefins, and it has been applied to cis-2-butene, cis-2-pentene, cis-3-hexene, cis-4-methyl-2-pentene, and norbornene. The alcohols realized exhibit optical purities in the range of 65 to 91%. Treatment of an excess of an olefin racemate with the reagent results in the preferential reaction of one of the components. In this way, racemic mixtures of 3-methylcyclopentene, 3-ethylcyclopentene, and 1-methylnorbornene have been converted into optically active olefin products. The absolute configuration of diisopinocampheylborane may be deduced from the known configuration of α-pinene. On the basis of a simple model for the hydroboration step it is possible to predict the absolute configuration of the optically active alcohols and olefins obtained in this asymmetric synthesis. © 1964, American Chemical Society. All rights reserved.