C(1→4)-linked disaccharides through carbonylative Stille cross-coupling

Abstract

A tinglucal tributyl[4,6- O-bis(t-butyl)silylidene-3- O-tris(isopropyl)silyl]tin 7 and a triflate derived from isolevoglucosenone (1 R,4 R,5 R)-4-benzyloxy-6,8-dioxabicyclo[3.2.1]oct-2-en-2-yl trifluoromethanesulfonate 10 undergo the carbonylative Stille condensation under special conditions requiring AsPh 3, LiCl, and powdered charcoal as co-catalysts to give a cross-conjugated dienone 6 in which the bicyclic alkene moiety is more reactive than the glucal alkene moiety. This allows the regio- and stereoselective hydrogenation of the bicyclic alkene moiety giving an enone 21 that can be reduced stereoselectively to an allylic alcohol 22. Hydroboration of the glucal and bicyclic acetal opening generates a C(1→4) linked disaccharide 25 in which a protected form of β- d-glucopyranose is attached at position C(4) of a α- d-3-deoxy- ribo-hexopyranoside derivative via a ( S)-hydroxymethano linker.