65. “[6π+4π] Cycloadditions of 5-azoniafulvene ions with nitrones and azomethine imines.”
    Burger, U.; Bringhen, A. O.
    Tetrahedron Lett. 1988, 29, 4415-4418.

Nitrones as well as azomethine imines generated by the prototropic route from hydrazones are shown to add readily to the title iminium ions to give pyrrolo-annellated oxadiazine and triazine derivatives.

DOI : 10.1016/S0040-4039(00)80510-9