Cobalt‐Catalyzed Intermolecular [2+2] Cycloaddition between Alkynes and Allenes

In equal measure: A cobalt/diphosphine catalyst promotes a selective [2+2] cycloaddition reaction between an alkyne and an allene, affording a 3‐alkylidenecyclobutene with high regioselectivity. The reaction tolerates various internal alkynes, and mono‐ and disubstituted allenes with different functional groups, and can be achieved using a near equimolar mixture of the unsaturated reactants.

Abstract

An intermolecular [2+2] cycloaddition reaction between an alkyne and an allene is reported. In the presence of a cobalt(I)/diphosphine catalyst, a near equimolar mixture of the alkyne and allene is converted into a 3‐alkylidenecyclobutene derivative in good yield with high regioselectivity. The reaction tolerates a variety of internal alkynes and mono‐ or disubstituted allenes bearing various functional groups. The reaction is proposed to involve regioselective oxidative cyclization of the alkyne and allene to form a 4‐alkylidenecobaltacyclopentene intermediate, with subsequent C−C reductive elimination.

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