Site-selective carbamoylation of carbohydrates catalyzed by SnCl2/Me2SnCl2 leading to complementary selectivity†

This work reports SnCl₂/Me₂SnCl₂-catalyzed site-selective carbamoylation of carbohydrates with a broad substrate scope, associated with mild reaction conditions, good selectivity and high isolated yields (using a flash column). In particular, the selectivity of carbamoylation resulting from the SnCl₂ method is complementary to that resulting from the Me₂SnCl₂ method in many cases. For several glycoside substrates containing cis-diol, their axial hydroxyl groups are selectively carbamoylated in the presence of the SnCl₂ catalyst, while their equatorial hydroxyl groups are selectively carbamoylated in the presence of the Me₂SnCl₂ catalyst. The substrate scope for the SnCl₂ method also includes glycosides containing 1,3-diol, but excludes glycosides containing trans-diol. The substrate scope for the Me₂SnCl₂ method can include glycosides containing trans-diol.