Arylethyne Bromoboration-Negishi Coupling Route to E- or Z-Aryl-Substituted Trisubstituted Alkenes of ≥98% Isomeric Purity. New Horizon in the Highly Selective Synthesis of Trisubstituted Alkenes

摘要

The hitherto unprecedented palladium-catalyzed cross-coupling of (Z)-β-bromo-β-arylethenylboranes can be made to proceed satisfactorily through (1) the use of highly catalytically active bis(tri-terr-butylphosphine)palladium or dichloro[N,N-bis-(2,6-diisopropylphenyl)imidazol-2-yl](m-chloropyridine)palladium and (2) conversion of the dibromoboryl group to the (pinacol)boryl group. Thus, a wide variety of carbon groups can be used to substitute bromine in ≥ 98% stereo- and re-gioselectivity, while suppressing the otherwise dominant β-debromoboration. Together with the alkyle-thyne-based protocols, the alkyne bromoboration-Negishi coupling tandem process has emerged as the most widely applicable and highly selective route to trisubstituted alkenes including those that are otherwise difficult to access.