SUGAR VINYLTIN DERIVATIVES - STABLE PRECURSORS OF SUGAR CARBANIONS

Sugar acetylenes 4a-4f were treated with tri-n-butyltin hydride at 140 -degrees in the presence of AIBN. Acetylenes 4a-4e were easily convert ed into cis vinyltin derivatives 5a-5e which isomerized under these co nditions to the more stable trans isomers 6a-6e in overall yield 70-90 %. The reaction of isopropylidene-alpha-D-xylo-hex-5-yno-1.4-furanose (4f) with Bu3SnH led almost exclusively to cyclization product 7 (as a mixture of three isomers); the expected compounds 5f\6f were obtained in 5% yield. Reaction of acetylene 4f with Bu3SnCu(Bu)CNLi2 (Lipshutz reagent) led in low yield to 6f and tri-n-butyltin acetylene 11 in th e ratio 1:4.