Bifunctional Squaramide-Catalysed Asymmetric Michael/Hemiketalization/Retro-Aldol Reaction of Unsaturated Thiazolones with α-Nitroketones: Synthesis of Chiral 4-Acyloxythiazole Derivatives

An efficient and practical organocatalytic asymmetric cascade Michael/hemiketalization/retro-aldol reaction of unsaturated thiazolones with α-nitroketones by using cyclohexanediamine-derived bifunctional squaramide as the catalyst has been developed. Under mild conditions, a broad range of chiral 4-acyloxythiazole derivatives were obtained in high yields (up to 98% yield) with excellent enantioselectivities (up to 95% ee). Meanwhile, a few synthetic transformations have been demonstrated. (Figure presented.).