'I5 21 P f YW product detected ('H NMR spectroscopy) in photolyses of the diene 13 conducted down to-80" C, in yields varying between 5% and 15%. However, when photolysis of the diene 13 was carried out in THF containing 20% w/v of isobenzofuran (15) a mixture of four C, H, O/isobenzofuran cycloadducts was obtained, together with the phthalimide 14 and the head to head photodimer 22 of i~ obenzofuran.'~ The adducts ...