Palladium-Catalysed Norbornene-Mediated Regioselective Direct C-H Glycosylation of Free (N-H) Pyrrole Derivatives

A palladium-catalyzed norbornene-mediated regioselective direct C-H glycosylation of free N-H pyrrole and electron-deficient pyrrole derivatives has been developed. The reaction involves the use of a Pd-II catalyst and norbornene as a transpositional co-catalyst, in which a pyrrole- and norbornyl-fused palladaheterocycle forms as the key intermediate. The 2-substituted pyrroles, and other 2,3-disubstituted pyrroles underwent the selective C5 glycosylation. This reaction is compatible with various types of glycosyl chlorides including D-mannose, L-rhamnose, D-mannofuranose, and D-ribofuranose. The viability of this strategy is showed by gram-scale, various synthetic transformation and functionalization.