Cyclic β-enaminones bearing secondary amino group react with 4-substituted benzenediazonium tetraphenylborates in dichloromethane to form substituted bicyclic [1, 3, 2λ4] oxazaborines The oxazaborines rearrange, on heating to 200° C in the absence of solvent or in DMF or DMSO, to isomeric 2H-[1, 2, 4, 3λ4] triazaborines. Previously prepared [1, 3, 2λ4] oxazaborines derived from acyclic β-enaminones bearing secondary amino ...