Scheme 3.

Synthesis of 2-chloropurine derivatives 6a and 6b. Reagents and conditions: (i) EtC(OEt)3,1 h, MW 160 °C; (ii) t-BuNH2, NMP, 2 h, MW 160 °C; (iii) 3,4-DHP, PTSA cat., EtOAc, 6 h, 60 °C

Synthesis of 2-chloropurine derivatives 6a and 6b. Reagents and conditions: (i) EtC(OEt)3,1 h, MW 160 °C; (ii) t-BuNH2, NMP, 2 h, MW 160 °C; (iii) 3,4-DHP, PTSA cat., EtOAc, 6 h, 60 °C