Ruthenium(II)-Catalysed sp2 C–H Bond Functionalization by C–C Bond Formation

Abstract : The selective catalytic activation/functionalization of sp2 C–H bonds is expected to improve synthesis methods by better step number and atom economy. This chapter describes the recent achievements of ruthenium(II) catalysed transformations of sp2 C–H bonds for cross-coupled C–C bond formation. First arylation and heteroarylation with aromatic halides of a variety of (hetero)arenes, that are directed at ortho position by heterocycle or imine groups, are presented. The role of carboxylate partners is shown for Ru(II) catalysts that are able to operate profitably in water and to selectively produce diarylated or monoarylated products. The alkylation of (hetero)arenes with primary and secondary alkylhalides, and by hydroarylation of alkene C=C bonds is presented. The recent access to functional alkenes via oxidative dehydrogenative functionalization of C–H bonds with alkenes first, and then with alkynes, is shown to be catalysed by a Ru(II) species associated with a silver salt in the presence of an oxidant such as Cu(OAc)2. Finally the catalytic oxidative annulations with alkynes to rapidly form a variety of heterocycles are described by initial activation of C–H followed by that of N–H or O–H bonds and by formation of a second C–C bond on reaction with C=O, C=N, and sp3 C–H bonds. Most catalytic cycles leading from C–H to C–C bond are discussed