Part I 2+2 Photocycloaddition Reactions Of N-acylindoles With Alkenes Part Ii Photochemical Reactions In Supercritical Carbon Dioxide

Part I. Irradiation of 2-methyl, 3-methyl and 2,3-dimethyl substituted N-acylindoles in the presence of alkenes results in the formation of {dollar}\lbrack{dollar}2+2{dollar}\rbrack{dollar} cycloadducts which contain cyclobutane rings. The regiochemistry of the major product in all cases examined was found to be the result of initial bond formation from the 2-position of the N-acylindole to the less substituted terminus of the alkene. The quantum yield of cycloadduct formation was determined for the photocycloaddition reaction of the N-benzoyl derivatives with methyl acrylate and for the N-carboethoxy derivatives with 2-methylpropene. The reaction efficiency was found to be dependent on two factors. The first of which is the quantum yield of intersystem crossing for each N-acylindole, which decreases with methyl-substitution on the indole ring. The second factor is the fraction of 1,4-biradical intermediates which close to form products in competition with fragmentation to starting materials. This fraction was found to be insensitive to the placement of a methyl group at the 2- or 3-position of the N-acylindole ring but was found to decrease upon placement of methyl groups at both the 2- and 3-position of the N-acylindole ring.;Part II. The photo-Fries rearrangements of 1-naphthyl acetate and N-carboethoxy-2-methylindole were investigated in supercritical carbon dioxide. These photolyses proceed via a solvent-caged singlet radical pair to result in products derived from in-cage recombination as well as cage-escape product formation. In supercritical CO{dollar}\sb2{dollar} the relative yield of the cage-escape products decreases dramatically as the pressure is decreased in the near critical region. This observation was interpreted in terms of an increase in the strength of the solvent cage near the critical point. The variation in the observed relative product ratios for each system provide evidence for the phenomenon of solvent-solute clustering in the near critical region of supercritical carbon dioxide