SELECTIVE NUCLEOPHILIC SUBSTITUTION AND PREFERENTIAL EPOXIDE FORMATION

The tri-O-methanesulfonyl derivatives of methyl β-D-xylopyranoside, methyl β-L-arabinopyranoside, and methyl α-L-arabinopyranoside undergo selective substitution at C-4, when heated with sodium azide in N,N-dimethylformamide, to yield 4-azido derivatives with inversion of configuration at C-4. The resultant 4-azido-2,3-di-O-methanesulfonyl derivatives were converted, by reaction with sodium methoxide, into 2,3-anhydro compounds whose configurations were assigned by nuclear magnetic resonance analysis. The mechanism of epoxide formation is discussed.