Exploring Cooperative Effects in Oxidative NHC Catalysis: Regioselective Acylation of Carbohydrates

The utility of oxidative NHC catalysis for both the regioselective and chemoselective functionalization of carbohydrates is explored. Chiral NHCs allow for the highly regioselective oxidative esterification of various carbohydrates using aldehydes as acylation precursors. The transformation was also shown to be amenable to both cis/trans diol isomers, free amino groups, and selective for specific sugar epimers in competition experiments. Efficiency and regioselectivity of the acylation can be improved upon using two different NHC catalysts that act cooperatively. The potential of the method is documented by the regioselective acylation of an amino‐linked neodisaccharide. Sweet and selective! Various sugar derivatives, including amino sugars, are acylated with complete selectivity for O‐acylation over N‐acylation using oxidative N‐heterocyclic carbene (NHC) catalysis (see scheme). Secondary alcohols in sugars are differentiated with high selectivity and the concept of using two different NHCs in NHC catalysis is introduced.