1,3-dimethoxy-5-methylene-1,3-cyclohexadiene compounds with leaving groupsat C6: Generation, solvolytic reactivity, and their importance in the photochemistry of 3,5-dimethoxybenzyl derivatives

The photochemistry of 3,5-dimethoxybenzyl compounds with the leaving groups acetate (1a), chloride (1b), bromide (1c), iodide (1d), diethyl phosphate (1e), and trimethylamine (1f), as the chloride, was examined by both produc t studies and flash photolysis. The isomeric triene, 5-methylene-1,3-cycloh exadiene derivative was observed for the acetate (2a), diethyl phosphate (2 e) and trimethylammonium chloride (2f). The solvolysis of these derivatives , 2, was examined in alcohol solvents and the rate correlation with Y-OTS v alues gave m = 0.47 (2a) and 0.63 (2e), suggesting S(N)1 reactivity but wit h an early transition state. Quantum yields for formation of 2a and 2e indi cated that these trienes play only a minor role (similar to 16%) in the ove rall photochemistry of the corresponding arylmethyl substrates.