Intramolecular photocycloaddition 2-naphthyl

Me and co-workers studied the intramolecular photocycloaddition of naphthyl groups in poly(l-vinylnaphthalene) (335) in cyclohexane, benzene, and dichloromethane [338], In cyclohexane, the reaction proceeds via first-order kinetics to a high conversion of 70%, whereas in dichloromethane, the reaction levels off at a very low conversion of 20%. Quenching and sensitizing experiments proved that the Mplet mechanism is predominant in cyclohexane, whereas in dichloromethane, a singlet mechanism is predominant. The addition of trifluo-roacetic acid to the illuminated sample restores the initial absorbance. 

Intramolecular Photocycloaddition of N—P4—A. Although the photocycloaddition of anthracene [85-100] and that of naphthalene [65-67,80-82] have been extensively studied, until recently relatively little has been reported on the cross-photocycloaddition between an anthracene and a naphthalene moiety [101-110], The main reason for this is the large difference in the quantum yields between the photocycloaddition of anthracene and the cross-photocycloaddition of anthracene and naphthalene. Thus, bichromophoric molecules with anthryl as one chromophore and naphthyl as the other generally undergo intermolecular an-thryl-anthryl cycloaddition rather than intramolecular cross-cycloaddition when irradiated. 

The anthracenes (188), which have a 3,5-dialkoxybenzyloxymethyl substituent on the 9-position, undergo quantitative (4jt + 4ji) intramolecular photocycloaddition to yield (189). " The process is thermally reversible, and (189) is readily converted to the diketone (190) on treatment with acid. In the presence of acid, the linked naphthyl and resorcinyl moieties in (191) undergo (2ji -I- 2jt) photoaddition with 300 nm radiation to give the tetrahydrofuran derivatives (192) by the route outlined in Scheme 3." The reaction also occurs in the absence of acid for (191) with R = -0-(CH2)2-0Me, but the quantum efficiency is reduced by 35-fold. The products (192) are labile under 254 nm radiation and undergo a novel photoextrusion of acetaldehyde to yield (193) by the pathway... 

The marked excess-energy dependence of the fluorescence-decay characteristics of tetracene vapour has again been interpreted in terms of the Sx - S0 internal-conversion process being enhanced by population of higher vibrational levels of the Sx state.67 The process has been observed directly in the case of pentacene by the recognition of transient absorption bands ascribed to hot SQ levels produced in the internal conversion.68 Non-linear absorption in the laser photolysis of anthracene,69 the intramolecular photocycloaddition reaction of l-(9-anthryl)-3-(l-naphthyl)propane,80 and the quenching of fluorescence of aromatic hydrocarbons by caesium chloride81 have been reported. 

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