Allenes In Manganese(I)-Catalyzed C-C Activation And A Strategy For Cascade Ring Expansion

Transition metal-catalyzed C-C bond functionalization has recently been identified as an increasingly versatile tool for organic syntheses, as otherwise unreactive functionalities can be used as efficient handles for synthetic manipulations. This work describes site-selective manganese(I)-catalyzed C-C hydroarylations of heteroarenes with substituted allenes. The C-C activations are efficiently catalyzed by MnBn(CO)(5) and afford 1,2,3-tri-substituted arenes with notable diastereoselectivity. Moreover, the ring-expansion reaction proceeds via a C-C allylation/Michael addition cascade, providing challenging 8-membered carbocycles, thus highlighting the unique characteristics of the MnBn(CO)(5) complex. Mechanistic studies reveal that the organometallic C-C activation occurs faster than typical C-H activations, thus providing a complementary approach to well-established methodologies for late-stage diversification.