Chemistry of Group 13 element-transition metal linkage — the platinum- and palladium-catalyzed reactions of (alkoxo)diborons

The metal-catalyzed borylation of alkenes, alkynes, and organic electrophiles with BB compounds was developed for the synthesis of organoboronic esters from simple organic substrates. The platinum(0)-catalyzed addition of bis(pinacolato)diboron to alkenes and alkynes stereoselectively yielded cis-bis(boryl)alkanes or cis-bis(boryl)alkenes. The addition of diboron to 1,3-dienes with a platinum(0) complex afforded a new access to the cis-1,4-bis(boryl)butene derivatives which are a versatile reagent for diastereoselective allylboration of carbonyl compounds. The cross-coupling reaction of diborons with aryl and vinyl halides or triflates, and allyl chlorides or acetates was found to yield aryl-, vinyl-, and allylboronates in high yields in the presence of a base and a palladium catalyst, which provides the first one-step procedure for the synthesis of organoboronic esters from organic electrophiles. The mechanisms and the synthetic applications of these reactions are discussed.