Synthesis of Propargyl Boranes via Silver Catalyzed Insertion of Alkynyl Carbene into B-H Bond

A silver-catalyzed insertion reaction of alkynyl carbenes derived in situ by decomposition of alkynyl N-nosylhydrazones, into a B-H bond is reported. This protocol emerges as a straightforward synthesis of various propargylic boron compounds with up to 95 % yield. The operationally simple method exhibits high functional group tolerance and produces a variety of propargyl boranes which are synthetically useful building blocks. Deuterium labelling experiment and DFT studies show that the reaction proceeds via insertion of alkynyl Ag-carbene into the B-H bond and generation of silver carbene occurs in the rate-determining step.