One-Pot Synthesis of Glycosyl-β-azido Ester via Diazotransfer Reaction Toward Access of Glycosyl-β-triazolyl Ester

A concise
and efficacious one-pot protocol for the synthesis of
novel glycosyl-β-azido ester 3 from glycosyl olefinic
ester 1 under mild conditions has been devised. The β-aminoester,
formed by the conjugate addition of ammonia on olefinic ester, undergoes
a metal-catalyzed diazotransfer reaction to furnish glycosyl-β-azido
ester. The optimized conditions for diazotransfer reaction indicate
that imidazole-1-sulphonyl azide and K2CO3 give
the best results in the presence of ZnCl2. A diverse range
of novel regioselective triazolyl glycoconjugates 6a–u have been achieved in high yields via 1,3-dipolar cycloaddition
of compound 3 with various alkynes in the presence of
CuI/DIPEA. Structures of all the compounds have been elucidated using
IR, NMR, MS, and elemental analysis, and four of them (3a, 3b, 4b, and 6a) have also
been characterized by single crystal X-ray diffraction analysis.