Unexpected reactions of (1R)2,3,4,6-tetra-O-acetyl-1-azido-D-galactopyranosyl cyanide and the derived carboxamide with triphenylphosphine

Article abstract of DOI:10.1016/S0040-4020(97)01055-7

Staudinger reaction of acetylated (1R)-1-azido-D-galactopyranosyl cyanide (1) with triphenylphosphine in diethyl ether led to the isolation of a crystalline phosphazide (2), unprecedented in carbohydrate chemistry. Spontaneous decomposition of 2 in toluene furnished the mixture of the unsaturated lactone 4, as minor product, and two major products: the triphenylphosphoranylidene derivatives of (2Z,4Z)-3-cyano-4,6-diacetoxy-2,4-hexadienoic amide (5), and (2E,4Z)-triacetoxy-2,4-hexadienoic amide (6), respectively, owing to an unusual pyranoid ring opening between C-5 and the pyranose oxygen. The carboxamide analogue (10) of 1 underwent a regular phosphinimine formation affording the equilibrium mixture of both anomers 11 and 12.