Concerning the mechanism of the reaction of methyllithium with methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside to form 4,6-O-benzylidene- 1,2-didehydro-1,2-dideoxy-2-methyl-D-ribo-hexopyranose

Abstract

Evidence supports the view that methyllithium, which contains no iodide or bromide ions as competitors, reacts with methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside to form, first, methyl 4,6-O-benzylidene-2-deoxy-2-methyl-α-D-altropyranoside. The latter compound then reacts with excess methyllithium to form 4,6-O-benzylidene-1,2-didehydro-1,2-dideoxy-2-methyl-D-ribo-hexopyranose by loss of methyl alcohol.A synthesis of methyl 4,6-O-benzylidene-2-deoxy-2-methyl-α-D-altropyranoside is given.The reactions of excess lithium iodide, bromide, and chloride with both methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside and methyl 2,3-anhydro-4,6-O-benzylidene-α-D-mannopyranoside are described.