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.