Study On Mannich Reaction Induced By Radical Cation Salts And Catalyzed By InCl₃.4H₂O

In this paper, we carefully studied the Mannich reaction between silyl enol ethers, ketones and aromatic imines induced by radical cation and InCl₃·4H₂O. A series of important compounds were synthesized, giving the following results:1. Tris(4-bromophenyl)aminium hexachloroantimonate (TBPA⁺.) can induce the Mannich reaction of aromatic imines and silyl enol ethers, producing a series of ?-amino ketones derivatives in high selectivity. We proposed a single electron transfer mechanism supported by several evidences.2. Based on the results obtained, we further optimized the reaction conditions in order to perform the synthesis of 4-piperidones. We found InCl₃·4H₂O as a Lewis acid could efficiently catalyze this tandem Mannich reaction producing 4-piperidones in high yields together with high selectivity, which promoted the applications of this reaction towards the synthesis of heterocyclic compounds containing nitrogen.