ACETONATION OF ALDOSE DIETHYL THIOACETALS

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Abstract
Acetonation of hexose diethyl thioacetals using copper sulphate catalyst gave rise to 5,6-O-substituted products. The exception was D-galactose diethyl thioacetal, which underwent some 4,5-O-substitution. D-Threose and 2,3-di-O-methyl-D-galactose diethyl thioacetals also underwent predominant α-terminal substitution although some β-terminal substitution took place, particularly with the latter thioacetal. Acetone – sulphuric acid caused preferential α-T acetonation of D-threose and 2,3-di-O-methyl-D-galactose diethyl thioacetals. The product from D-threose diethyl thioacetal contained 90% of the 2,3-O-isopropylidene and 10% of the 3,4-O-isopropylidene derivatives.D-Glucurono-δ-lactone diethyl thioacetal in acetone – sulphuric acid acetonated mainly on the 2,4- positions although a smaller proportion of 4,5-O-isopropylidene derivative was present.

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