Transition Metal‐Free Regio‐ and Stereo‐Selective <i>trans</i> Hydroboration of 1,3‐Diynes: A Phosphine‐Catalyzed Access to (<i>E</i>)‐1‐Boryl‐1,3‐Enynes
Swetha Jos, Connor Szwetkowski, Carla Slebodnick, Robert Ricker, Ka Lok Chan, Wing Chun Chan, Udo Radius, Zhenyang Lin, Todd B. Marder, Webster L. Santos
Abstract
We report a transition metal-free, regio- and stereo-selective, phosphine-catalyzed method for the trans hydroboration of 1,3-diynes with pinacolborane that affords (E)-1-boryl-1,3-enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3-diyne framework as unambiguously established by NMR and X-ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle.