Regio- and Diastereoselective [3 + 2]-Spiroannulation of Benzoxazines with Chalcones: A Rh(III)-Catalyzed Redox-Neutral Approach to α‑Aroyl Spiro-Indanamines

We report an atom-economic Rh­(III)-catalyzed [3 + 2]-spiroannulation
reaction between cyclic ketimines and α,β-unsaturated
carbonyl compounds, allowing the synthesis of novel spirocycles with
concomitant generation of three stereogenic centers in one pot. The
reaction does not require any silver additives or external oxidants
and is believed to proceed in a redox-neutral manner. A broad substrate
scope with good functional group tolerance permitted the synthesis
of a vast spectrum of spirocyclic 1,4-benzoxazine derivatives containing
polysubstituted α-aroyl-indanamines in good to excellent yields
with high diastereoselectivity.