Photochemical Rduction of 2-Bromo-4,4-dimethyl-2-cyclohexenone

Article abstract of DOI:10.1002/hlca.19820650736

The photochemical behaviour of 2-Bromo-4,4-dimethyl-2-cyclohexenone (1) was studied in 2-propanol and cyclohexane.In both solvents (n-?*)-excitation followed by intersystem crossing leads to population of a low-lying triplet (T₁) state, which can be quenched by 1,3-cyclohexadiene but does not undergo chemical transformation efficiently, (?-?*)-Excitation affords 4,4-dimethyl-2-cyclohexenone (2) as the only product.While in 2-propanol 2 is formed in 60percent from the S₂-state and in 40percent from the T₂-state, in cyclohexane reduction occurs exclusively from this upper triplet state.The T₂-state can also be populated via energy transfer using acetonee or benzene as senzitizer.The mechanistic dissimilarities for the reduction of excited 1 in either 2-propanol or cyclohexane are discussed.