Asymmetric Mannich Reaction of Aryl Methyl Ketones with Cyclic Imines Benzo[e][1,2,3]oxathiazine 2,2‐Dioxides Catalyzed by Cinchona Alkaloid‐based Primary Amines |
| |
Authors: | Xiao‐Yu Cui Hui‐Xin Duan Dr Yongna Zhang Prof?Dr You‐Qing Wang |
| |
Institution: | Key Laboratory of Polyoxometalate Chemistry of Henan Province, Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan, P. R. China |
| |
Abstract: | Aryl ketones represent problematic substrates for asymmetric Mannich reactions due to a large steric hindrance exhibited by such compound species. A highly enantioselective direct Mannich reaction of aryl methyl ketones with cyclic imine benzoe]1,2,3]oxathiazine 2,2‐dioxides could be successfully carried out utilizing a combination of cinchona alkaloid‐derived primary amines with trifluoroacetic acid (TFA); the primary amines feature a superior catalytic efficacy over secondary amines with a variety of sterically hindered carbonyl compounds as substrates. The reaction proceeded well with various cyclic imines in 89–97 % ee and with various aryl methyl ketones in 85–98 % ee. Moreover, the aryl carbonyl of a Mannich product could be transformed to ketoxime, which further undergoes a Beckmann rearrangement to produce an amide compound while maintaining enantioselectivity. |
| |
Keywords: | asymmetric catalysis ketones Mannich reaction nitrogen heterocycles organocatalysis |
|
|