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.