Isoxazolium anhydrobase

In 2003, irradiation of isoxazolium anhydrobase in acetonitrile has been reported to give a novel (3-lactam system such as a 4,5-dihydrofuroazetidinone (yield 60%) [174], The mechanistic interpretation of this result involved a photochemical N-O bond cleavage, followed by the formation of a cyclopropanone intermediate (Scheme 75). 

Scheme 75 Synthesis of P-lactam system by photorearrangement of isoxazolium anhydrobase...

Photochemical rearrangement of the readily prepared isoxazolium anhydrobase 345 yielded the novel bicyclic 4,5-dihydrofuroazetidinone system 27 (Equation 38). A mechanism for the rearrangement has been proposed <2003TL9247>. 

---