Wittig/B─H insertion reaction: A unique access to trisubstituted Z -alkenes

Abstract

The Wittig reaction, which is one of the most effective methods for synthesizing alkenes from carbonyl compounds, generally gives thermodynamically stable E -alkenes, and synthesis of trisubstituted Z -alkenes from ketones presents notable challenges. Here, we report what we refer to as Wittig/B─H insertion reactions, which innovatively combine a Wittig reaction with carbene insertion into a B─H bond and constitute a promising method for the synthesis of thermodynamically unstable trisubstituted Z -boryl alkenes. Combined with the easy transformations of boryl group, this methodology provides efficient access to a variety of previously unavailable trisubstituted Z -alkenes and thus provides a platform for discovery of pharmaceuticals. The unique Z- selectivity of the reaction is determined by the maximum overlap of the orbitals between the B─H bond of the borane adduct and the alkylidene carbene intermediate in the transition state.

Fe-catalyzed B–H and Si–H insertion reactions of gem-dihaloalkanes

“…5,6 Particularly noteworthy is the transition metal-catalyzed insertion of carbenes into B–H bonds, which has emerged as a potent strategy for C–B bond construction. 7,8 In this context, various carbene precursors, including diazo compounds, 9 alkynes, 10 sulfoxonium ylides, 11 and cyclopropenes, 12 have been successfully employed, providing facile access to organoboranes with high yields and, in some instances, excellent enantioselectivities (Fig. 1a).…”