Synthesis and hydroboration of a 3-C-methylene derivative of 2-amino-2-deoxy-D-glucose

Opening of the epoxide ring of methyl 3,3′-anhydro-2-benzamido-4,6- O -benzylidene-2-deoxy-3- C -(hydroxymethyl)-α- D -allopyranoside ( 1 ) with sodium iodide, in the presence of acetic anhydride and p -toluenesulfonic acid, gave methyl 3- O -acetyl-2-benzamido-4,6- O -benzylidene-2-deoxy-3- C -(iodomethyl)-α- D -allopyranoside ( 2 ). Reduction of 2 with powdered zinc in buffered N,N -dimethylformamide gave methyl 2-benzamido-4,6- O -benzylidene-2,3-dideoxy-3- C -methylene-α- D - ribo -hexopyranoside ( 3 ) in 92% yield. Treatment of 1 with zinc in acetic acid containing sodium iodide afforded 3 directly in 90% yield. Hydroboration-oxidation of 3 gave a mixture of methyl 2-benzamido-4,6- O -benzylidene-2-deoxy-3- C -methyl-α- D -glucopyranoside ( 6 ), and the corresponding 3-deoxy-3- C -(hydroxymethyl) derivatives ( 4 ). Chromatographic separation of the isomers afforded one of the 3-deoxy-3- C -(hydroxymethyl) 3-epimers as a pure oil, and 6 as an impure oil. Acetylation of the former with acetic anhydride in pyridine gave the 3-deoxy-3 C -(acetoxymethyl) derivative ( 5 ), and acetylation of 6 with acetic anhydride containing p -toluenesulfonic acid gave crystalline methyl 3- O -acetyl-2-benzamido-4,6- O -benzylidene-2-deoxy-3- C -methyl-α- D -glucopyranoside ( 7 ).