Selectivity in the acylation of partially silylated hydroxy polymers - a study with trimethylsilyl cellulose and model compounds

Abstract

Acylation of partially trimethylsilylated cellulose, glycerol (1), 1,3-bis(trimethylsiloxy)-2-propanol (2), methyl-2,3,4,6-tetrakis-O-trimethylsilyl-α-D-glucopyranoside (10) and methyl-2,3,4-tris-O-trimethylsilyl-α-D-glucopyranoside (11) either with acyl chlorides/triethylamine at room temperature or with acyl chlorides at elevated temperature in the absence of an acid scavenger has been studied. Selective acylation of free hydroxy groups has been found with acyl chloride/amine, though complete conversion of free hydroxy groups of cellulose could not be achieved under these conditions. High temperature acylation, however, results in an unselective reaction of free hydroxy groups and trimethylsilyloxy groups. Trans-silylation takes place and chlorination is found in the reaction of 1 and 2. Carbohydrates were not chlorinated under these conditions, silyl cellulose, however, is strongly depolymerized.