Organoboranes. 30. Convenient procedures for the synthesis of alkyl- and alkenylboronic acids and esters

Article abstract of DOI:10.1021/om50004a008

Alkyl- and alkenyldibromoborane-dimethyl sulfide complexes, readily obtained by the hydroboration of alkenes and alkynes with dibromoborane-dimethyl sulfide (HBBr₂-SMe₂), react with water, giving the corresponding boronic acids, and with alcohols and glycols to give the corresponding esters. Various procedures have been developed for the preparation of boronic esters with primary and secondary alcohols, glycols, and tertiary alcohols. Boronic acids react with primary and secondary alcohols reversibly to form the corresponding esters. The equilibrium may be conveniently displaced in favor of ester by carrying out the reaction in pentane, from which the water component separates. This procedure does away with the necessity of azeotrope distillation of a ternary mixture, extensively used previously for the esterification of boronic acids.