CHIRAL SYNTHESIS VIA ORGANOBORANES. 2. RAPID REACTION OF BORONIC ESTERS OF VERY HIGH OPTICAL PURITY WITH LITHIUM ALUMINUM HYDRIDE. FACILE REACTION OF ESSENTIALLY OPTICALLY PURE BORINIC ESTERS WITH LITHIUM MONOETHOXYALUMINOHYDRIDE. A NOVEL AND QUANTITATIVE SYNTHESIS OF LITHIUM MONOALKYL- AND DIALKYLBOROHYDRIDES OF ESSENTIALLY 100% OPTICAL PURITY.

Article abstract of DOI:10.1021/ja00288a031

Boronic esters of very high optical purity readily react with lithium aluminum hydride in diethyl ether-pentane at 0 degree C to form the corresponding lithium monoalkylborohydrides of very high optical purity and dialkoxyalane. Under these reaction conditions the dialkoxyalane generally precipitates quantitatively from solution. The reaction is essentially quantitative and is broadly applicable to a representative variety of essentially optically pure boronic esters. Addition of 1 mol equiv of very high optically pure borinic esters to lithium monoethoxyaluminohydride in diethyl ether at 0 degree C results in a facile and rapid precipitation of the dialkoxyalane as a solid, producing the corresponding lithium dialkylborohydride of very high optical purity in quantitative yield. The reaction is quite general, proceeds without detectable racemization, and is applicable to essentially optically pure borinic esters of widely varied structural requirements.