The synthesis and transformations of 3‐ethoxycarbonyl‐2‐isothiocyanatopyridine. Pyrido[2,3‐ d ]pyrimidines and some azolopyrido[2,3‐ d ]pyrimidines

3‐Ethoxycarbonyl‐2‐isothiocyanatopyridine ( 2 ), prepared from 2‐amino‐3‐ethoxycarbonylpyridine ( 1 ) by the thiophosgene method, was converted into thiouretanes 3 and 4 , 1,4‐disubstituted thiosemicarbazide 6 , thioamide 8 , and thioureas 15 and 18 . The compounds 2 and 3 were converted into bicyclic pyrido[2,3‐ d ]pyrimidines 5, 9, 10, 11, 12, 16 , and 17 , and tricyclic azolopyrido[2,3‐ d ]pyrimidines 13 and 14 .