One-step synthesis of glycosidic spiroketals from 2,3-epoxybutyl glycoside derivatives

Abstract

The cis-epoxides 12 and 13, made by epoxidation of (Z)-4′-hydroxbut-2′-enyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside, have been converted into the corresponding 4′-iodides which, on treatment with tributyltin hydride under UV light, gave the crystalline spiroketal 21(68%, from the iodide 14 derived from 12) and four analogous isomeric products (from the iodide 16 derived from 13). The differences in the selectivities of the reactions are attributed to hydrogen bonding in intermediate anomeric radicals. In both cases, 4′-oxobutyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside 24 was produced as a by-product.