Efficient synthesis of purine analogues: an FeCl3–SiO2-promoted cyclization reaction of 4,5-diaminopyrimidines with aldehydes leading to 6,8,9-trisubstituted purines

6,8,9-Trisubstituted purine analogues were efficiently synthesized via cyclization of 6-chloro-4,5-diaminopyrimidines and various aldehydes promoted by FeCl3–SiO2. Fe(III) chloride on silica gel has a dual role of a dehydration agent and an oxidant, and was conveniently removed during work-up by filtration.