Selective Construction of Spiro or Fused Heterocyclic Scaffolds via One-pot Cascade Reactions of 1-Arylpyrazolidinones with Maleimides.

Presented herein is a controllable selective construction of spiro or fused heterocyclic scaffolds through the one-pot cascade reactions of 1-phenylpyrazolidinones with maleimides. To be specific, succinimide spiro pyrazolo[1,2-a]pyrazolones were effectively formed via [4 + 1] spiroannulation of 1-phenylpyrazolidinones with maleimides through simultaneous C(sp2)-H bond activation/functionalization and intramolecular cyclization along with the traceless fusion of the pyrazolidinonyl unit into the final product. In this reaction, air acts as a cost-effective and environmentally sustainable oxidant to assist the regeneration of the Rh(III) catalyst. Alternatively, succinimide-fused pyrazolidinonylcinnolines were formed from the same starting materials through an initial [4 + 1] spiroannulation followed by base-promoted skeleton rearrangement of the in situ formed spiro product without isolation. Notable features of these protocols include easily tunable selectivity, broad substrate scope, cost-effective and sustainable oxidant, excellent atom economy, and facile scalability.