Über die orthoesterbildung als konkurrenzreaktion zur glykosylierung

Abstract

1,2-(Alkyl orthoacetates) (orthoesters) were obtained in good yields from acetylated cis-glycosyl halides and alcohols in tetrahydrofuran in the presence of silver salicylate. The scope and the possible mechanism of the reaction were investigated. The presence of an intermediate oxonium ion ( 13) derived from the sugar derivative and tetrahydrofuran was deduced, from the occurrence of 4-bromobutyl 2,3,4,6-tetra- O-acetyl-β- d-glucopyranoside as a by-product of the reaction, and from semi-quantitative kinetic investigations. After an intramolecular reaction of this ion to form an acetoxonium ion ( 14), the reaction with an alcohol yields the orthoester ( e.g. 1- 7). In a similar manner, and in concurrence with direct glycosylation, ortho esters and products arising from orthoesters may be formed in the usual glycoside synthesis, using the reaction just described with the solvent or other nucleophiles.