A masked diboron in Cu-catalysed borylation reaction: highly regioselective formal hydroboration of alkynes for synthesis of branched alkenylborons

The use of a masked diboron as a boron source in the presence of a Cu-N-heterocyclic carbene (NHC) catalyst enables alkyl-, aryl-, heteroatom- and silyl-substituted terminal alkynes to undergo a-selective formal hydroboration to give diverse branched alkenylboron compounds exclusively. Synthetic potential of this alpha-selective hydroboration has been demonstrated by total synthesis of pharmaceutically significant bexarotene and LG100268.