A study on the scope of the photochemical 1,3-migration of oximino groups in β,γ-unsaturated oximes and oxime derivatives

While the aza-di-π-methane rearrangement is the normal photoreactive behaviour of β,γ-unsaturated imines and oxime acetates, the results obtained in this study show that 1,3-migrations of acetoxyimino groups in β,γ-unsaturated oxime acetates takes place only when all the parameters are correct. The rearrangement takes place when there is a quaternary carbon separating the two π-systems and when one of the radical centres in the intermediate cyclobutyl 1,4-biradical is stabilized by conjugation with a phenyl ring. Suppression of the free rotor effect also helps to promote the reaction. These criteria are fulfilled in compounds 1a and 7a. The reaction was extended to the β,γ-unsaturated oximes l b and 7b where again the 1,3-migration of the oximino group took place.