Synthetic Applications of C-2 Substituted Glucal

Abstract

This report concerns the development of a synthetic approach towards synthesis of seven-membered septanosides, such as, substituted oxepanes from protected 2-hydroxyglycals. Important precursors to the synthesis of the septanosides is 1,2-unsaturated sugars. This report summarizes the work towards preparation of 1,2-unsaturated sugars, namely, hydroxy glycal ethers, from available bench-top sugars and some of its synthetic applications. The synthetic approach relies on initiating the synthesis from judiciously protected glucopyranoside, having reactive anomeric sites, is subjected through a series of reactions. An unasaturated sugar synthon is prepared from methyl α-D-glucopyranoside, through O-benzylation, acetolysis, and bromination, followed by an elimination reaction. The reactive site is amenable for reactions, such as, cyclopropanation, epoxidation and aziridination. Reactions leading to the formation of 2-hydroxyglycal are optimized. The hydroxyl glycal ethers are also resourceful synthons for further synthetic conversions and preparation of target-oriented natural and un-natural products. In relevance to the aims of the current project, an objective is to utilize the suitably functionalized hydroxyl glycal ether for ring expansion to seven membered septanoside ring followed by branching out at C-2 carbon of the septanosides.