Synthesis of nitrooxazoles

A reaction sequence involving halogenation and replacement of the halo substituent by a nitro group using dinitrogen tetraoxide has led to a general, convenient route to 5‐nitrooxazoles. Reaction schemes employing both bromine and iodine as the halo substituent have been investigated; however, the method using iodine preceded by a mercuration step affords a better overall yield in the range of 20–50%. Both 2‐ and 4‐nitro‐oxazoles can be prepared by this latter sequence, though in lower overall yields (4–12%).