Chemoselective 3-O-alkylation of L-ascorbic acid under phase transfer catalysis

Abstract

A detailed investigation for synthesis of chemo-selective 3-O-alkylation of L-ascorbic acid under phase transfer catalysis has been carried out. All the compounds were fully characterized by infra red (IR), NMR and microanalysis. Reaction of 5,6-O-isopropylidene-L-ascrobic acid with one equivalent of corresponding alkylating agent and tetrabutyl ammonium iodide as phase transfer catalyst in biphasic system (water:ethyl acetate, 1:1) afforded the 3-O-alkyl-5,6-O-isopropylidene-L-ascorbic acid derivatives (2a-f) in moderate to good yield as a sole product. Under this reaction condition formation of 2-C-alkylated and 2,3-di-O-alkylated product was not observed. Furthermore, present protocol allowed preparation of 2,3-di-O-alkyl and differentially protected 2,3-di-O-alkyl derivatives under mild reaction conditions at room temperature in a one-pot reaction. Key words: 3-O-Alkylation, L-ascorbic acid, phase transfer catalysis, chemoselective alkylation.