Suzuki reactions of extended scope: the 9-MeO-9-BBN variant as a complementary format for cross-coupling

While the Suzuki coupling has gained paramount importance, the basic set-up of the reaction has remained essentially unchanged for decades. It consists of the palladium-catalyzed coupling of organoboron reagents with aryl- or alkenyl halides, -sulfonates or related electrophiles in the presence of a base. One of the few alternative formats for this transformation is the 9-MeO-9-BBN variant, which is distinguished by not requiring an added base as a promoter. Rather, polar organometallic reagents RM (R = Me, alkyl, aryl, heteroaryl, alkenyl, alkynyl etc. ) are first intercepted with 9-MeO-9-BBN to give the corresponding borinate complexes, which then pass the R-group onto an organopalladium complex generated in situ as the electrophilic partner. This procedure allowed the structural reach of the Suzuki coupling to be extended, and served in a host of advanced applications, most notably for elaborate spsp 2 and sp 3 sp 2 coupling processes. The 9-MeO-9-BBN variant complements the classical Suzuki reaction, in that it does not require any added base and allows R groups to be transferred which are beyond the scope of the conventional set-up.