N-Heterocyclic Carbene-Catalyzed Aza-Michael–Mannich–Lactamization Cascade for the Enantioselective Synthesis of Pyrazoloquinolin-3-ones
Sayan Shee, Deeptanu Sarkar, Akkattu T. Biju
Abstract
The enantioselective synthesis of functionalized pyrazoloquinolin-3-ones via N-heterocyclic carbene-catalyzed cascade reaction of α-bromoenals with 2-aminoaryl N -tosyl hydrazones is reported. The in situ-generated α,β-unsaturated acylazoliums underwent an aza-Michael–Mannich–lactamization sequence to afford the tricyclic products bearing three contiguous stereocenters, including a sterically demanding quaternary stereocenter with high enantioselectivity. The unprotected amine-triggered aza-Michael pathway over the competing amidation pathway is noteworthy.
Topics & Concepts
StereocenterChemistryEnantioselective synthesisCarbeneMannich reactionCatalysisMichael reactionAmine gas treatingSteric effectsOrganocatalysisCombinatorial chemistryStereochemistryOrganic chemistryN-Heterocyclic Carbenes in Organic and Inorganic ChemistryCatalytic Cross-Coupling ReactionsSynthetic Organic Chemistry Methods