Ti-Catalyzed Oxidative\nAmination Using Anilines

In this report, Ti-catalyzed transfer\nhydrogenation from anilines\nto alkynes is leveraged to generate nitrenes from anilines in the\nTi-catalyzed [2 + 2+1] synthesis of <i>N-</i>aryl pyrroles.\nWhile there are myriad methods for accessing nitrene reactive intermediates\nin chemical synthesis, methods for the direct transformation of amines\ninto nitrene equivalents are uncommon. This transfer hydrogenation-coupled\n[2 + 2 + 1] pyrrole synthesis is catalyzed by a recently reported <i>bis</i>(phenoxide) Ti complex, (TPO)Ti(NMe<sub>2</sub>)<sub>2</sub> (TPO = (3,3″-di<i>tert</i>-butyl-5,5″-dimethyl-[1,1′:2′,1″-terphenyl]-2,2″-bis(olate)).\nPreliminary mechanistic insight indicates that a balance of the competition\nbetween alkyne insertion into titanacycle Ti–C bonds versus\nTi–C aminolysis at several points along the catalytic cycle\nis critical for productive catalysis over unwanted side reactions,\nsuch as alkyne hydroamination or alkyne cyclotrimerization.