The formylation at the anomeric carbon of the model sugars 2,3,4,6-tet
ra-O-benzyl-D-glucopyranose and 2,3:5,6-di-O-isopropylidene-D-mannofur
anose is carried out by addition of 2-lithiothiazole to the correspond
ing lactones followed by reductive dehydroxylation and thiazole to for
myl deblocking.