1,4-Butanediol as a reducing agent in transfer hydrogenation reactions

1,4-Butanediol is able to deliver two equivalents of H-2 in hydrogen-transfer reactions to ketones, imines, and alkenes. Unlike simple alcohols, which establish equilibrium in the reduction of ketones, 1,4-butanediol acts essentially irreversibly owing to the formation of butyrolactone, which acts as a thermodynamic sink. It is therefore not necessary to use 1,4-butanediol in great excess in order to achieve reduction reactions. In addition, allylic alcohols are reduced to saturated alcohols through an isomerization/reduction sequence using a ruthenium catalyst with 1,4-butanediol as the reducing agent. Imines and alkenes are also reduced under similar conditions.