Synthesis and functionalization of 2-hydroxypyrimido[4,5-b][1,4]oxazine

An efficient synthesis of pyrimido[4,5-b][1,4]oxazines is realized using 5-bromouracil. Substitution in the 2-position was performed by palladium-mediated cross-coupling reactions (Suzuki, Stille and carbon–nitrogen bond forming process) and by SNAr reactions. Microwave-heating is also used for high-speed synthesis.