C-Glycosylcrotylboronates for the Synthesis of Glycomimetics

The stereoselective synthesis of E- and Z- isomers of a C- mannosyl crotylpinacolboronate via Ni-promoted reactions on an allylic acetate and a diene precursor, respectively, is described. The E- and Z- isomers reacted with 1,2-O-isopropylidene glyceraldehyde in the presence or absence of (R)- and (S)- TRIP catalysts, to give predominantly 3,4-anti and 3,4-syn crotylation products, respectively, with moderate to high facial selectivity. These products were transformed to biologically relevant C-manno-disaccharides.