Enantio- and Z-Selective δ-Hydroarylation of Aryl-Substituted 1,3-Dienes via Rh-Catalyzed Conjugate Addition.

Abstract

Metal-catalyzed enantioselective conjugate arylations of electron-poor alkenes are highly selective processes for C(sp2)-C(sp3) bond formation. δ-Selective hydroarylations of electron-poor 1,3-dienes are less well developed and reactions that deliver high enantioselectivity while giving single alkene isomer products are elusive. Here we report the Rh-catalyzed δ-arylation of aryl-substituted 1,3-dienes that gives nearly exclusive Z-1,4-addition products (generally with >95 : 5 positional and geometrical selectivity). This remote functionalization provides access to chiral diarylated alkenes from readily available precursors poised for further functionalization, including in the synthesis of bioactive molecules. Mechanistic studies suggest that protonolysis of a Rh-allyl intermediate generated by diene insertion into a Rh-aryl is the turnover limiting step and occurs by an inner-sphere proton transfer pathway.