Cyclization reactions of 1,3‐dibromopropan‐2‐ol, 2,3‐dibromopropan‐1‐ol and 1‐bromomethyloxirane with 6‐amino‐2,3‐dihydro‐2‐thioxo‐4(1 H )‐pyrimidinone

The cyclization reactions, carried out in strongly‐ or weakly‐basic media, are described. Sometimes, 7‐amino‐2,3‐dihydro‐3‐hydroxymethyl‐5 H ‐thiazolo[3,2‐ a ]pyrimidin‐5‐one is separated out, together with 8‐amino‐3,4‐dihydro‐3‐hydroxy‐2 H ,6 H ‐pyrimido[2,1‐ b ][1,3]thiazin‐6‐one, as the principal product. A mechanism of reaction, during which the cyclizating agents are changed into oxirane derivatives, is proposed. The results of single‐crystal X‐ray investigations on 8‐amino‐3,4‐dihydro‐3‐hydroxy‐7‐nitroso‐2 H ,6 H ‐pyrimido[2,1‐ b ][1,3]thiazin‐6‐one (R = 0.035 for 1013 reflections), and on 7‐hydroxymethyl‐6,7‐dihydrothiazolo[3,2‐ a ][1,2,3]triazolo[4,5‐ d ]pyrimidin‐9(1 H )‐one (R = 0.027 for 1607 reflections) are reported.