Cross-coupling of Aromatic Aldehydes with N-(Amidobenzyl)benzotriazoles: An Alternative Route to α-Amidoketones

Background: Several transition-metal-catalyzed reactions have been used to synthesize biologically active α-amidoketones. These approaches involve inconvenient conditions or expensive catalysts. Alternative attempts based on transition-metal-free catalysts have also been reported including cross-coupling reaction of aldehydes with acylimines in the presence of thiazolium salt as an organic catalyst. We report herein the use of N,N-dimethylbenzimidazolium iodide which is a safe and recyclable organic pre-catalyst, along with N-(amidobenzyl)benzotriazoles as activated N-acylimines for this cross-coupling reaction. Method: N-(Amidobenzyl)benzotriazoles (9a-c) were prepared from benzamide, aromatic aldehydes and benzotriazole. N,N-Dimethylbenzimidazolium iodide (11) was easily prepared via the methylation reaction of benzimidazole. Cross-coupling reactions were carried out in refluxing THF in the presence of DBU and organo-catalyst 11 for 5 hours. Results: N,N-Dimethylbenzimidazolium-catalyzed cross-coupling reactions of various aromatic aldehydes (10a-f) with N-(amidobenzyl)benzotriazoles (9a-c) afforded α-amidoketones (12a-r) in good yields. Conclusion: An alternative approach for the synthesis of α-amidoketones based on organo-catalytic cross-coupling reaction of aromatic aldehydes with acylimines have been accomplished in high yields. Keywords: α-Amidoketones, N-(amidobenzyl)benzotriazoles, masked N-acylimines, N, N-dimethylbenzimidazolium iodide, organic catalyst, aldehyde.