Novel oxa-di-pi-methane and Norrish type I reactions in the S2 (pi,pi*) excited state of a series of beta,gamma-unsaturated ketones.

[reaction: see text] Beta,gamma-unsaturated methyl ketones with electron-withdrawing groups at the gamma-position of the ene moiety undergo ODPM rearrangements and Norrish type I reactions on direct irradiation at 254 nm. The results are consistent with the involvement of alkene S(2) (pi,pi*) as reactive excited states in these processes.