Synthesis of Organoboron Compounds via the Transition Metal-Catalyzed Addition and Coupling Reaction of (Alkoxo)diborons.

Transition metal-catalyzed additions and cross-coupling reactions of the metal-metal compounds have attracted considerable attention as direct routes to prepare various organometallic compounds. Although the corresponding reactions of boron compounds had not yet been well developed, we recently reported the first platinum (0) -catalyzed addition reaction of bis (pinacolato) diboron (1 d) to either terminal or internal alkynes to give cis-bis (boryl) alkenes. The addition of 1 d to 1, 3-dienes and alkenes with platinum (0) complexes afforded a new access to the cis-1, 4-bis (boryl) butene and bis- (boryl) alkane derivatives. The palladium (0) -catalyzed cross-coupling reactions of 1 d with aryl halides or triflates, and allyl chlorides or acetates gave the corresponding aryl- and allylboronates in high yields, which provides the first one-step procedure for organoboronic esters from organic electrophiles. Since (alkoxo) diborons are thermally stable and easily handled in air, the reagent can be useful as boron nucleophiles for cross-coupling reactions with organic halides. The mechanisms and the synthetic applications of those reactions are discussed.