[2-PHOTOCYCLOADDITION OF 2-AMINOPROPENENITRILES AND T-BUTYLVINYLSULFIDE TO METHYL PHENANTHRENE-9-CARBOXYLATE(2])

With high regioselectivity electronically excited methyl phenanthrene- 9-carboxylate (4a) forms ''head to tail'' [2+2]-cycloadducts 5a-c and 6a by addition of 2-aminopropenenitriles 2a-c to its C9, C10 double bo nd. The stereoselectivity of this reaction is - at least for the addit ion of 2a to 4a - only moderate favouring the E- (or ''anti''-) adduct 5a. In the cases of 2-aminopropenentiriles 26, c the Z- (or ''syn''-) adducts 6b, c cannot be isolated. No primary cycloadduct at all but o nly the hydrolysis product 8 is observed in attempts of addition of 2d or 4a. The structure of the E-adduct 5a has been unambiguously confir med by a single crystal X-ray structural analysis which in turn allowe d the assignment of Z-geometry to 6a. While no cycloadditions are obse rved with 2-(t-butylthio) propenenitrile (9a), t-butyl vinylsulfide (9 b) is added successfully to 4a and the corresponding nitrile 4b with f ormation of ''head to head'' adducts 10a and 10b, respectively. A comb ination of both static and dynamic quenching of fluorescence of 4a by alkenes 2a, b, e and 9a, 6 has been observed, with the most efficientl y quenching alkenes 2e, 9a being totally ineffective in the cycloaddit ion. Partial quenching of the addition of 2a to 4a by octafluoronaphth alene (OFN) suggests that both the excited singlet and tripler stales of 4a participate in the ''head to tail'' cycloadditions.