Enantioselective Cobalt(III)-Catalyzed [4 + 1] Annulation of Benzamides: Cyclopropenes as One-Carbon Synthons

A chiral cyclopentadienyl cobalt(III)-catalyzed enantioselective [4 + 1] annulation of N-chlorobenzamides with cyclopropenes is reported. The cobalt catalyst engages in the C–H activation as well as promotes the C–C bond cleavage of the cyclopropene, rendering it as a one-carbon unit for the annulation. The reaction efficiently constructs biologically relevant chiral isoindolinones with selectivities of up to 99:1 er and >20:1 E/Z ratios. The cobalt(III) catalyst displays a unique orthogonal reactivity profile delivering [4 + 1] annulation products, whereas its rhodium(III) homologue engages in the more classical [4 + 2] annulation pattern. Computational studies reveal the origin of these reactivity divergences.