Switchable [4 + 3] or [3 + 3] Annulation of Pyrazolidinones with Diazoarylidene Succinimides for the Divergent Synthesis of Fused Benzodiazepines and Quinolines

Abstract

Presented herein are Rh(III)-catalyzed C–H bond activation-initiated switchable [4 + 3] and [3 + 3] annulation reactions of 1-phenylpyrazolidinone with diazoarylidene succinimide governed by subtle condition modulation. To be specific, with AgOAc as additive and hexafluoroisopropanol (HFIP) as solvent, a formal [4 + 3] annulation via C–H metalation, carbene formation, migratory insertion, 1,3-allyl migration, and reductive elimination takes place to furnish fused benzodiazepine. Swapping the additive to Zn(OAc)2 and the solvent to THF results in a formal [3 + 3] annulation through C–H metalation, carbene formation, migratory insertion, N–N bond activation, 1,3-allyl migration, reductive elimination, and proto-demetalation to furnish fused quinoline. In general, the reactions employ simple substrates, proceed under mild conditions, exhibit excellent functional group tolerance, and demonstrate good selectivity to deliver valuable products in good yields. Moreover, the synthetic utility of these methods is validated by gram-scale synthesis and product derivatization. Notably, the products thus obtained display potent anticancer activities.