The importance of ground state conformation in the photoisomerizations of protonated enones

The conformations of several protonated enones have been determined by low temperature 13 C nuclear magnetic resonance spectroscopy. Information on the ground state conformation has been used to understand the differences in the photochemistry of these systems. Photoisomerizations of 4 and 5 have been examined. In the case of 4, irradiation leads only to the formation of the Z isomer 16; protonated dihydrofuran 13 was not observed. In the case …