Synthesis of Alkylborohydrides by Addition of Alkoxides, Amides and Thiolates to the Corresponding Alkylboranes

Reaction of a metal alkoxide with a borane or an alkylborane does not form the corresponding alkoxyborohydride. Instead, the reaction produces a 1:1 mixture of a borate and a borohydride. This product mixture is an effective reducing agent for a variety of functional groups, such as: esters, halides, and azides. The reduction products can be isolated by a nonoxidative removal of the boron byproducts via precipitation with ethanolamine. Additionally, the alkoxide may be used in a catalytic manner, with a stoichiometric amount of dialkylborane, to reduce substrates such as esters that are normally inert to dialkylboranes. Similarly, metal amides and thiolates react with alkylboranes and produce a 1:1 mixture of the corresponding alkylborohydride along with amidoborates and thioborates respectively.

alkylborohydride synthesis - alkylborane metathesis - alkoxide - amide - thiolate