Mixed Diboration of Alkynes Catalyzed by LiOH: Regio- and Stereoselective Synthesis of cis-1,2-Diborylalkenes.

A diboration of terminal alkynes with an unsymmetrical diboron reagent pinBBdan has been achieved using LiOH as the catalyst in the presence of stoichiometric amounts of MeOH, affording 1,2-diborylalkenes with different boryl groups. The reaction proceeds in a highly regio- and stereoselective manner through cis-addition of pinBBdan to the C-C triple bond, with the Bdan moiety being incorporated at the internal position. By taking advantage of the different reactivities of the two boryl groups, the mixed diboration product can undergo the sequential, chemoselective cross-couplings with aryl bromides to form trisubstituted alkenes.