Selective ring closure to substituted pyrido[1,2-b]-as-triazinium salt
摘要:
Reaction of arylglyoxal with 1,2-diaminopyridinium salt 1 under acidic conditions afforded 2-aryl-pyrido[1,2-b]-as-triazinium salt 9 selectively, whereas cyclization of the same dioxo compound with 1-amino-2-iminopyridine 5 under neutral conditions - due to "umpolung" of the exo nitrogen atom - led exclusively to the 3-aryl isomer 8.