Oxidative Annulation of C-H Bonds with Alkynes via a Manganese(-I/I) Catalytic Cycle.

Abstract

An unprecedented catalytic system relying on a manganese(-I/I) catalytic cycle is reported for the oxidative annulation of aryl imidazolium salts with alkynes. Using earth-abundant manganese in place of precious metals, this reaction employs Mn(CO)5Br as a precatalyst, BnBr as an oxidant, and Me2Zn as a base, affording substituted imidazo [1,2-a]quinolin-10-ium salts in high yields. Mechanistic studies identify a key cyclomanganated intermediate and implicate a [Mn(CO)3]- species, confirming a unique Mn(-I/I) catalytic cycle. This system overcomes the limitations of redox-neutral mechanisms in conventional Mn(I) catalysis and offers a new paradigm for manganese-catalyzed C-H activation.

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