Spiroborate esters in the borane-mediated asymmetric synthesis of pyridyl and related heterocyclic alcohols

The effectiveness of several spiroborate ester catalysts was investigated in the asymmetric borane reduction of 2-, 3-, and 4-acetylpyridines under different reaction conditions. Highly enantiomerically enriched 1-(2-, 3-, and 4-pyridyl)ethanols and 1-(heterocyclic)ethanols were obtained using 1-10% catalytic loads of the spiroborate 5 derived from diphenylprolinol and ethylene glycol.