Hydroboration of Terminal Alkynes Catalysed by Sodium Triethylborohydride

Sodium triethylborohydride - commonly used as a reducing agent for hydroboration catalysts based on the first-row transition metal complexes with tridentate ligands, has been found a highly selective catalyst for hydroboration of terminal alkynes. Hydroboration of aromatic and aliphatic alkynes with pinacolborane in the presence of 10 mol% of NaHBEt3 proceeded in a highly selective manner to give (E)-vinylboronate esters with high yields, whereas ethynylsilanes seem to be less reactive in this process.