Organocatalysed Michael addition on arylmethylidenemalonates involving 4-(2-nitrophenyl)acetoacetate: diversity-oriented access to 8,9-dihydropyrido[1,2-a]indol-6(7H)-one and salicylate scaffolds

Abstract

Excellent diastereoselective (≤96 : 4) preparation of new functionalized 7,8,9-trisubstituted-8,9-dihydropyrido[1,2-a]indol-6(7H)-ones has been achieved in 61–81% yields through a one-pot reductive cycloaromatization–lactamization sequence reaction of Michael adducts using Zn/NH₄Cl as a reducing agent. In addition, one-pot synthesis of sterically demanding hexa-substituted salicylate derivatives has been successfully realized via a tandem reaction of alkylidene malonates or aldehydes with 2-nitrophenyl-β-keto ester under aerobic conditions using DBU as an organocatalyst.