Study of Direct N 7 Regioselective tert -Alkylation of 6-Substituted Purines and Their Modification at Position C 6 through O, S, N, and C Substituents.

A new N 7 direct regioselective method allowing the introduction of tert -alkyl groups into appropriate 6-substituted purine derivatives is developed. This method is based on a reaction of N -trimethylsilylated purines with a tert -alkyl halide using SnCl 4 as a catalyst. In this work, we study the structure and optimal reaction conditions leading to the N 7 isomer and in some cases also to the N 9 isomer. The main goal is devoted to preparing 7-( tert -butyl)-6-chloropurine as a suitable compound for other purine transformations. The stability of the tert -butyl group at the N 7 position is tested for classic model reactions, leading to the preparation of new 6,7-disubstituted purine derivatives, which is also interesting from the point of view of possible biological activity.