Abstract1,3‐Dimethyl‐6‐aminouracil 2 was converted into various 8‐N‐arylaminotheophyllines (2‐N‐arylamino‐4,6‐dimethylimidazo[4,5‐d]pyrimidine‐(4H,6H)‐5,7‐diones) 17 through reaction successively, with phosgeniminium chloride (N,N‐dimethyldichloromethyleniminium chloride) (1a), trimethylsilyl azide (4) and arylamines. Starting with the synthesis of the N,N‐dimethyl(1,3‐dimethyl‐4‐aminouracil‐5‐yl)chloromethyleniminium chloride (amide chloride) 3 this new route to the imidazo[4,5‐d]pyrimidine skeleton was shown to proceed via the formation of a very unstable N,N‐dimethyl‐(1,3‐dimethyl‐4‐aminouracil‐5‐yl)azidomethyleniminium chloride (amide azide) (8) which would undergo an in situ rearrangement into very likely, a 4‐amino‐5‐(chloroformamidin‐1′‐yl)uracil and/or related compounds of types 10. Depending on reaction conditions, the latter was proved to be a very good precursor of the 8‐dimethylaminotheophylline 11 as well.