Diastereoselective Spirocyclization of Cyclic N-Sulfonyl Ketimines with Nitroalkenes via Iridium-Catalyzed Redox-Neutral Cascade Reaction.

An Ir(III)-catalyzed [3 + 2] annulation of weakly coordinating N-sulfonyl ketimines with challenging α, β-unsaturated nitro olefins has been achieved via redox-neutral C-H functionalization in the presence of a catalytic amount of silver hexafluoroantimonate. The generation of three consecutive stereogenic centers in a single step via direct C-H functionalization is the prime feature of this methodology. A wide array of pharmaceutically relevant nitro-substituted spirocyclic benzosultams was synthesized with good to excellent diastereoselectivity as well as in high yield starting from easily accessible substrates.