Quaternary <i>N</i> -Heterobenzylic Carbon Centers via Allene-Mediated C–H Functionalization of Azines/Azoles: Ruthenium-Catalyzed Dearomative Addition-Hydrogen Auto-Transfer

Metal-catalyzed N -heteroaryl C–H functionalizations to form quaternary heterobenzylic carbon centers are described. Exposure of 1,1-disubstituted allenes to the ruthenium catalyst derived from RuHCl(CO)(PPh 3 ) 3 and Cy-BIPHEP results in generation of allylruthenium nucleophiles that engage in azine or azole C═N addition to deliver transient dearomatized homoallylic amidoruthenium complexes, which upon β-hydride elimination release products bearing quaternary N -heterobenzylic carbon centers with regeneration of the starting ruthenium hydride. The dearomative addition-β-hydride elimination pathway is corroborated by deuterium-labeling experiments and interception of the dearomatized amidoruthenium intermediate through its protonolytic cleavage by 2-propanol and conversion to the methanesulfonamide. Comparison of RuCl(η 3 -C 3 H 5 )(CO)(Cy-BIPHEP) vs RuCl(η 3 -C 3 H 5 )(CO)(BIPHEP), including single crystal X-ray diffraction and IR data, provides insight into the superior performance of the Cy-BIPHEP-modified catalyst.