Stereospecific (2π+2π) photocycloaddition of arylalkenes to pyrene via exciplex: formation of 1:1- and 2:1-cycloadducts

Irradiation of benzene solutions containing pyrene and electron-deficient arylalkenes such as E- and Z-methyl cinnamates afforded (2π+2π) photocycloadducts including 1:2-cycloadduct in high yields in a stereospecific and endo-selective manner. Sandwich-type singlet exciplexes between pyrene and arylalkenes were proposed as reactive intermediates.