Water-assisted diboron activation: efficient synthesis of alkyl 1,2-bis(boronates) and 1,1,2-tris(boronates)

Abstract

Multifunctionalization of easily accessible feedstocks namely alkenes and alkynes to synthesize polyboronate compounds represents an extremely useful process in organic synthesis. Herein, we disclose a method to access synthetically versatile alkyl 1,2-bis(boronates) and 1,1,2-tris(boronates) via metal- and base-free diboration and triboration of alkenes and alkynes, respectively, with bis(pinacolato)diboron (B₂pin₂) as the boron reagent, aided by water, which is yet unknown. This strategy's practicality and industrial importance are demonstrated by avoiding the use of stoichiometric amounts of base and its operational simplicity. This protocol demonstrates broad substrate scope and good functional-group tolerance on alkenes and alkynes. Preliminary mechanistic studies reveal the formation of tetrahydroxydiboron as an active boron reagent for these C–B bond formation reactions. The most striking feature of this procedure is the synthesis of multiboronate compounds without using any organic solvents and facile extractive workup.