The Use of Grignard Reagents in the Synthesis of Carbohydrates. I. The Synthesis of Deoxy and Branched-chain Deoxy Sugars

Two branched-chain deoxy sugars, methyl 5,6-O-cyclohexylidene-3-deoxy-2-C-methyl-β-d-arabino-hexofuranoside and its α-d-ribo isomer, were easily prepared by the one-step reaction of methyl 5,6-O-cyclohexylidene-3-O-mesyl-β-d-allofuranoside (3a) with methylmagnesium iodide. Similarly, the corresponding α-mesylate (4a) gave methyl 5,6-O-cyclohexylidene-3-deoxy-2-C-methyl-α-d-ribo-hexofuranoside. It was demonstrated that these reactions involved 1,2-hydride shifts. The reaction of 3a and 4a with t-butylmagnesium bromide yielded two deoxy sugars, methyl 5,6-O-cyclohexylidene-3-deoxy-β-d-arabino-hexofuranoside and the corresponding α-d-ribo isomer, respectively. Under certain reaction conditions with the Grignard reagents, the sulfonate (3a) afforded dimeric compounds, in which two furanose rings were directly bound with a carbon–carbon bond. A convenient method for the preparation of the sulfonates (3a and 4a) is also reported.