Intramolecular Cycloadditions of Photogenerated Azaxylylenes with Oxadiazoles Provide Direct Access to Versatile Polyheterocyclic Ketopiperazines Containing a Spiro-oxirane Moiety

Photogenerated
azaxylylenes undergo intramolecular cycloadditions
to 1,3,4-oxadiazole pendants, which are accompanied by concomitant
release of dinitrogen, yielding functionalized ketopiperazinoquinolinols
containing an oxirane moiety fused to the quinolinole moiety while
spiro-connected to diketopiperazine. These primary photoproducts are
reactive versatile intermediates which can be further derivatized
under nucleophilic SN1- or SN2-like ring opening
of the oxirane moiety. The oxidized quinolinones undergo new rearrangements
under the conditions of the Schmidt reaction, leading to unprecedented
triazacanoindolinones.