Synthesis of functionalised pyrido[4,3-b][1,4]oxazine and imidazo[1,2-a]pyridine derivatives

Ethyl 3,4-dihydro-2H-pyrido[3,2-b][1,4]oxazine-2-carboxylate derivatives were obtained from 3-hydroxy-2-aminopyridine and ethyl 2,3-dibromopropanoate. Reduction of thiolactam obtained from the lactam gave the corresponding ethyl 2H-pyrido[3,2-b][1,4]oxazine-2-carboxylate. The use of ethyl 2-chloro-3-oxopropanoate with 2-amino-3-hydroxypyridine or 3-amino-4-hydroxypyridine led, respectively, to imidazo[1,2-a]pyridine derivatives or ethyl pyrido[4,3-b][1,4] oxazine-2-carboxylate.