Approaches to higher-carbon sugars, based on the use of sugar-derived, stabilized Wittig reagents

Abstract

1-(1,2:3,4-Di- O-isopropylidene-α- d-galactopyranuronyl)imidazole, obtained by treating the corresponding diacetal of α- d-galactopyranuronic acid with 1,1-carbonyldiimidazole, reacts with methylenetriphenylphosphorane to give (1,2:3,4-di- O-isopropylidene-α- d-galactopyranuronyl)-(triphenylphosphoranylidene)methane ( 3) as a crystalline, stable Wittig reagent. Compound 3 reacts with aldehydo sugars to provide α,β-unsaturated ketones, preponderantly as the E isomers. The α,β-unsaturated ketones react with lithium dimethyl cuprate to afford an ∼3:1 mixture of the 1,4-addition products, and with methylmagnesium chloride to give a 12:1 mixture of the tertiary allylic alcohols methyl 5-deoxy-5- C-[7-deoxy-1,2:3,4-di- O-isopropylidene-6- C-methyl- d(and l)- glycero-α- d- galacto-heptos-7( E)-ylidene]-2,3- O-isopropylidene-β- d-ribofuranoside, which undergoes an oxidative rearrangement when treated with pyridinium chlorochromate.