Phosphine-catalyzed hydroboration of propiolonitriles: access to ( E )-1,2-vinylcyanotrifluoroborate derivatives.

We report an organocatalytic trans hydroboration of 3-substituted-propiolonitriles. In the presence of catalytic amounts of tributylphosphine and pinacolborane, regioselective hydroboration of the internal triple bond proceeded in a stereoselective fashion under mild conditions to afford the corresponding ( E )-1,2-vinylcyanoborane derivatives. The mechanism is proposed to occur through a 1,2-phosphine addition instead of a canonical 1,4-conjugate addition pathway.