Macrocyclic 5-bromouracil derivatives: synthesis and transformation of a uracil ring

Cyclization of 1,3-bis(ω-bromoalkyl)-5-bromouracil with p-methoxybenzylamine or sodium sulfide led to a series of pyrimidinophanes containing heteroatoms in bridges. An unusual behaviour of the 5-bromouracil ring, namely its contraction into hydantoin units during the cyclization reactions with p-methoxybenzylamine was observed. Sodium sulfide does not affect the 5-bromouracil ring, and no transformation products were observed in the synthesis of pyrimidinophanes with sulfur bridges. A possible reaction mechanism is given.