Abstract Irradiation (λ> 370 nm) of 4, 4-dimethoxy-2, 5-cyclohexadienone (1 a) in benzene affords mainly the ketene acetal 4 a, which then undergoes further rearrangement. The carbomethoxycyclopentenones 6 and 7 were isolated in modest yields (10–15). It is conceivable that the latter results from decomposition of the unobserved bicyclohexenone 5 a, the formation of which could be expected by analogy to eg 1 c [RIGHTWARDS ARROW] ...
