Synthesis and Reactions of Phosphine-Boranes

Abstract

New methods for the synthesis of phosphine-boranes including optically active ones have been established. Diphenylphosphine-borane and methyldiphenylphosphine-borane reacted with various electrophiles to give phosphine-borane derivatives having a functional group. Diastereomerically pure secondary phorphine-boranes. (Sp)-and (Rp)-menthyloxyphenylphosphine-boranes were prepared from dichlorophenylphosphine. These secondary phosphine-boranes underwent stereospecific alkylation and arylation reactions. The phosphorus-oxygen bond of the resulting phosphine-boranes was reductively cleaved by lithium naphthalenide in an almost quantitative yield with virtually net retention of configuration. A new and efficient route to bidentate phosphine ligands with homochiral phosphine center has been established on the basis of these stereochemical studies on the substitution reactions at chiral phosphorus. Functionalizations of the boranato group of phosphine-boranes have been investigated. Trialkylphosphine-boranes reacted with methanesulfonic acid or trifluoromethanesulfonic acid with evolution of hydrogen The resulting sulfonates were subjected to nucleophilic substitution reactions with various nucleophiles including carbon nucleophiles. A new phosphine-borane having a P-B-P-B-P-B-P-B bond linkage was synthesized. © 1993, The Society of Synthetic Organic Chemistry, Japan. All rights reserved.