Synthesis and tautomerism of ethyl 2‐(2‐benzothiazolyl)‐2‐(6‐purinyl)acetate and related compounds

Reaction of 6‐chloro‐9 H ‐(2‐tetrahydropyranyl)purine ( 2d ) with the sodium salt of ethyl benzothiazole‐2‐ace‐tate ( 1 ) in dimethylformamide effects condensation of the two compounds (with loss of sodium chloride) to give the corresponding ethyl diarylacetate 4 (35%), present largely as an enol chelate tautomer. Isolated as a by‐product is 6‐(2‐aminophenyl‐1‐thio)‐9 H ‐(2‐tetrahydropyranyl)‐purine (4%), formed via opening of the thiazole ring. Removal of the tetrahydropyranyl protective group from 4 occurs by treatment with p ‐toluenesulfonic acid in aqueous ethanol to produce ethyl benzothiazole‐2‐(6‐purinyl)acetate (80%), existent largely as two enol chelate isomers. Spectral data for the various products are presented. An attempt to use 6‐chloro‐9‐acetyl‐9 H ‐purine in place of 2d in the first reaction gives acetylation of 1 instead of condensation.