Photobromination of Some Pyranose Derivatives and Reactions of the Brominated Products

Abstract

The light-catalysed reactions of some per-O-acylated aldopento- and hexo-pyranose derivatives with N-bromosuccinimide and with bromine were investigated, and products of bromination at C-5 were obtained. Photobromination of acylated aryl glucopyranosides was similarly studied and compounds having the bromine incorporated at C-5 were again the major reaction products; an acylated alkyl glucopyranoside gave a product resulting from initial abstraction of the hydrogen atom at C-1. A number of alkenes derived from 5-bromo compounds are reported, and their conformations in solution have been ascribed from 1H n.m.r. data. The hydrolysis of a 5-bromohexose derivative gave a 1,5-dicarbonyl compound, and reactions of this hex-5-ulose derivative with alcohols and thiols and attempted syntheses from it of functionalised cyclopentanes were studied. The former investigations gave access to acylated alkyl 5-chloro-D-glucopyranosides. Treatment of the 5-bromo- and 5-chloro-D-glucopyranoside derivatives with lithium aluminium hydride has provided a new route to L-idopyranoside derivatives. A 5-bromopentopyranose compound was employed in attempted approaches to resolved chiral crown ethers and “double-headed” nucleosides after its elimination and substitution reactions had been investigated.