Photochemistry of Tetracyclo[7.2.1.04,11.06,10]dodeca-2,7-diene Based Systems

Abstract

The feasibility of intramolecular [2+2]- and [6+2]- or [6+6]-photocycloaddition reactions in tetracyclo[7.2.1.0^4,11.0^6,10]dodecadienes and mono- or bis-benzoanellated systems as well as the stability of the respective photoisomers are discussed on the basis of structural and calculated thermochemical data. Sensitized excitation of conformationally modified dienes of type B-1 (see Scheme 1) yields, uniformly, the stable [2+2]-adducts. [6+2]-additions in benzo-enes B-2 are observed upon direct excitation and on account of their thermal lability, the photoproducts were only characterized indirectly. At temperatures down to —75°C, no [6+6]-adduct formation has been observed in B-3 face-to-face dibenzo substrates.