Photocyclisation of enamides. Part III. Photocyclisation of N-benzoylenamines of cyclohexanone and 2-substituted cyclohexanones

Abstract

Irradiation of methanolic solutions of N-benzoylenamines [(I), (VIII), and (IX)] of cyclohexanone and 2-sub-stituted cyclohexanones (R = Me or CO₂Et) resulted in stereoselective photocyclisation to give trans-octahydrophenanthridones [(II), (X), and (XI)]. However irradiation of the enamide (Ia) in the presence of iodine afforded the hexahydrophenanthridone (V), which was also obtained from the 6-bromo-enamide (VI) upon irradiation. The conjugated oxo-enamides (XIV) afforded the hexahydrophenanthridones (XV) even under non-oxidative conditions.