Purines. XIII. Ring Opening of 3-Alkyladenines with Carbobenzoxy Chloride : Transformation into 8-Hydroxylated Adenines

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Treatment of 3-ethyladenine (Ia) with carbobenzoxy chloride in a mixture of acetonitrile and aqueous sodium bicarbonate resulted in the cleavage of the imidazole ring to form a compound presumed to be IVa, which was recyclized to 8-hydroxy derivative Va when heated in acetic acid. Carbobenzoxylation of 3-benzyladenine (Ib) under similar conditions gave Vb directly. The 8-hydroxy structure of Va, b was confirmed by hydrogenolysis of Vb leading to 6-amino-8-hydroxypurine (VIII), and the 3-alkyl structure was established by hydrogenolysis of Va to 6-amino-3-ethyl-3H-purin-8-ol (VIa), chlorination of VIa to give 8-chloro derivative VIIa, and hydrogenolysis of VIIa to Ia using hydrogen and palladium-on-charcoal.