基于醋酸铑、磺酸和手性亚磺酰胺基脲共催化的α-重氮酯与酰胺不对称N—H插入反应研究

Asymmetric N—H Insertion Reaction of α-Diazoesters and Carbamates Co-catalyzed by Dirhodium Acetate, Sufonic Acid and Chiral Sulfonamide Urea

研究了醋酸铑[Rh2(OAc)4]、手性亚磺酰胺基脲和非手性磺酸共催化的α-重氮酯与酰胺化合物的不对称N—H插入反应.研究发现α-重氮酯在醋酸铑催化下形成金属卡宾,该金属卡宾与酰胺反应生成潜手性活泼叶立德中间体.在催化剂量的手性亚磺酰胺基脲和非手性磺酸存在下,潜手性叶立德中间体发生不对称质子化,合成了手性α-氨基酸衍生物.反应过程中,手性亚磺酰胺基脲和非手性磺酸作为"手性质子梭"催化不对称质子迁移从而实现了反应的对映选择性控制.该方法发展了非手性铑、手性亚磺酰胺基脲和非手性磺酸不对称共催化体系,为合成α-氨基酸衍生物提供了一种新途径,反应收率最高可达84%,对映选择性最高可达77%.

The enantioselective N—H insertion of α-diazoesters and carbamates provides a potentially attractive approach to α-amino acid derivatives. Herein, a novel cooperative catalytic system of achiral dirhodium（Ⅱ） acetates, chiral sulfonamide urea and achiral sulfonic acid was developed for asymmetric N—H insertion reactions. Prochiral ammonium ylide intermediates, generated in situ from α-diazoesters and carbamates initiated by dirhodium（Ⅱ） acetate, underwent asymmetric protonation with a considerable enantioselectivity in the presence of chiral sulfonamide urea and achiral sulfonic acid as co-catalysts. The co-catalysts of chiral sulfonamide urea and achiral sulfonic acid were considered as a chiral proton shuttle assisting the asymmetric proton transfer process to control the enantioselectivity. This methodology provides an efficient and mild approach to α-amino acid derivatives in high yields （up to 84% yield） with moderate enantioselectivity （up to 77% ee）.