Synthesis and photochemical transformations of new butadiene chromophores: The influence of the nature and position of chlorine substituent on the photoinduced behaviour

The photochemical behaviour of mono- and dichloro-substituted butadiene derivatives was studied at low concentrations. These compounds display diverse photochemical behaviour. The α-chloro derivatives photocyclize to give six-membered ring photoproducts. p-Chloro-substituted butadienes undergo intramolecular [2 + 2] cycloaddition followed by formation of benzobicyclic structures. The steric hindrance of chlorine(s) in α-position(s) cause a greater deviation from planarity, relative to p-substitution, and shift conformer equilibria and affects the reaction pathways and yields.