ABSTRACT
A general method has been developed for the formation of glycosyl chlorides and bromides from picolinic esters under mild and neutral conditions. Benchtop stable picolinic esters are activated by a copper(II) halide species to afford the corresponding products in high yields with a traceless leaving group. Rare ß glycosyl chlorides are accessible via this route through neighboring group participation. Additionally, glycosyl chlorides with labile protecting groups previously not easily accessible can be prepared.
Subject(s)
Bromides/chemical synthesis , Chelating Agents/chemistry , Chlorides/chemical synthesis , Esters/chemistry , Glycosides/chemical synthesis , Picolines/chemistry , Bromides/chemistry , Chlorides/chemistry , Glycosides/chemistry , Molecular StructureABSTRACT
Glycosyl isoquinoline-1-carboxylate was developed as a novel benchtop stable and readily available glycosyl donor. The glycosylation reaction was promoted by the inexpensive Cu(OTf)2 salt under mild reaction conditions. The copper isoquinoline-1-carboxylate salt was precipitated from the solution and thus rendered a traceless leaving group. Surprisingly, the proton from the acceptor was absorbed by the precipitated metal complex and the reaction mixture remained at neutral pH. The copper-promoted glycosylation was also proven to be completely orthogonal to the gold-promoted glycosylation, and an iterative synthesis of oligosaccharides from benchtop stable anomeric ester building blocks becomes possible under mild reaction conditions.
ABSTRACT
A catalytic method is developed for the diastereoselective acylation of the anomeric hydroxyl group in diverse carbohydrates to form either α- or ß-anomeric esters. While exclusive formation of the ß-isomer was observed in most sugar substrates with one enantiomer of the chiral catalyst, moderate to high α-selectivity was obtained by using the other enantiomer of the chiral catalyst. The resulting α- and ß-anomeric esters have very different reactivity toward a reduction reaction.
