New syntheses of d- and l-glycero-d-manno-heptoses

Three methods for the synthesis of the title compounds starting from benzyl 2,3,4-tri-O-benzyl-α- d -manno-hexodialdo-1,5-pyranoside (7 have been elaborated. Conversion of 7 into the cyanohydrin followed by reduction to give the amine and then deamination gave a derivative of l -glycero- d -manno-heptose in low yield. Condensation of 7 with 2-methylfuran gave two stereoisomeric 6-C-(2-methyl-5-furyl) derivatives. The preponderant stereoisomer was ozonised and then reduced to give a derivative of d -glycero- d -manno-heptose. Condensation of 7 with allyloxymethylmagnesium chloride gave derivatives of both heptoses in good yield and with an l -glycero d -glycero ratio of 3.2:1. Deprotection of these derivatives gave the heptoses in high yield.