Abstract Reaction of the title methyl glycoside 5 with methanolic sodium methoxide afforded mainly the isomeric α- d - erythro -hex-3-enopyranoside derivative 13 , formed by migration of the double bond from C-2 to C-3, together with 1,5-anhydro-4,6- O -benzylidene-2-deoxy-3- O -methyl-2- C - p -tolylsulfonyl- d - ribo -hex-1-enitol ( 7 ) and the methyl 4,6- O -benzylidene-3- O -methyl-2- C - p -tolylsulfonyl-α-