Access to 1,1-Diborylalkenes and Concomitant Stereoselective Reactivity

Gem-diborylalkenes have emerged as efficient reagents for selective cross-coupling reactions, reduction approaches and Michael additions. The synthesis of 1,1-diborylalkenes involves condensation of polyborated compounds with aldehydes or ketones followed by B–O elimination, geminal diboration of 1,1-dihaloalkenes, 1-haloalkenes or terminal alkynes, dehydrogenative borylation of alkenes, borylation of alkynylboronates and hydroboration of alkynylboronates. These new sets of reactions are general for a wide range of substrates and they can be understood to have complementary mechanisms.