Purines. XXXVIII. A General Synthesis of 7,9-Dialkyladeninium Salts from 9-Alkyladenines by Regioselective Alkylation : Utilization of an N^6-Alkoxy Group as a Control Synthon

A detailed account is given of the general synthetic route to 7,9-dialkyladeninium salts (16-18) from N^6-alkoxy-9-alkyladenines (type 5 or 11-13), readily obtainable from 9-alkyladenines in three steps involving N(1)-oxidation, O-alkylation, and Dimroth rearrangement. Alkylations of N^6-methoxy-9-methyladenine (5) and 9-alkyl-N^6-benzyloxy-adenines (11-13) with MeI, EtI, and PhCH_2Br in AcNMe_2 produced the corresponding 7-alkylated derivatives (15 and 19-21), together with small amounts of the N^6-alkylated isomers (6,8,and 9). Catalytic hydrogenolysis of the former compounds with hydrogen and Raney Ni yielded 7,9-dialkyladeninium salts (16-18).