Copper-Catalyzed Quadruple Borylation of Terminal Alkynes to Access sp 3 -Tetra-Organometallic Reagents.

Copper-catalyzed regioselective quadruple borylation of terminal alkynes has been developed employing a copper catalyst generated from CuI and dcpe (1,2-bis(dicyclohexylphosphino)ethane). A wide range of terminal alkynes undergo this multi-borylation reaction to afford the corresponding 1,1,2,2-tetraborylalkanes in high yields. Mechanistic studies reveal that this quadruple borylation reaction proceeds through copper-catalyzed sequential double 1,2-diborylation of alkynes and 1,2-diborylalkene intermediates. This protocol represents the most straightforward and atom-economic approach to prepare sp 3 -tetra-organometallic reagents from readily accessible alkynes with commercially available copper catalysts.