Grahame N. Taylor

Intramolecular photocycloaddition reactions of phenyl–vinyl bichromophoric systems

The Intramolecular photocycloaddition reactions of several phenyl–vinyl bichromophoric systems are reported. 5-Phenylpent-1-ene and allyl benzyl ether both yielded meta-cycloadducts derived from 1,3- and 2,6-attack of the vinyl group on to the phenyl moiety, whereas 3-phenylpropyl vinyl ether and 2-phenoxybut-1-ene gave products which reflected 1,3- and 2,4-, and 2,4-attack, respectively. In contrast, the major mode of reaction from phenethyl vinyl ether involved 2,5-cycloaddition and the 1,4-intramolecular cycloadduct structure was assigned to the sole photoisomer of 2-phenoxyethyl vinyl ether. Quantum efficiencies were very variable ranging from 0.005 to 0.11; polymeric materials were formed in all cases and were the major products from the two phenoxy-compounds. The reactions are discussed in terms of previous mechanistic proposals for benzene–ethylene photocycloaddition processes and conformation of the excited-state molecules.

Photocycloaddition reactions of phenyl–vinyl bichromophoric systems

The efficiency and mode of intramolecular photocycloaddition of the bichromophoric molecules Ph[CH2]mO[CH2]nCHCH2 are shown to depend on the values of m and n and on the overall chain length; the importance of ethereal oxygen at the various positions in the chain is demonstrated by comparison of the results with those obtained from hydrocarbon systems.

Stereochemistry of the 1,2-photocycloadducts of vinyl ethers and benzene

Die Addukte aus Olefinen an Benzol (I) der allgemeinen Struktur (II) werden hinsichtlich ihrer Isomeren und deren Trennung untersucht.

The stereochemistry of 1,2-photocycloaddition of vinylic compounds to benzene

The stereochemistry of the 1,2-photocycloaddition of benzene to acrylonitrile, methyl acrylate, methyl methacrylate, methyl vinyl ketone, ethyl vinyl ether, butyl vinyl ether, 2,3-dihydropyran, and 2,3-dihydro-1,4-dioxin has been investigated. The evidence indicates that exo-1,2-adducts are formed exclusively from all these vinylic compounds except the acrylates and methyl vinyl ketone, which gave mixtures of exo- and endo-stereoisomers.

Photochemical reactions of benzene derivatives with electron-donor ethylenes

The photoreactions of ethyl vinyl ether with benzonitrile, toluene, and anisole are reported and compared with those involving benzene as the arene. As the difference in ionisation potential between the addends decreases, the ortho-cycloaddition reaction becomes less favoured and the meta-process predominates. Regio- and stereo-isomers are formed in both photo-cycloaddition reactions. The meta-cycloadditions to toluene and anisole are exclusively 2,6- as are those of 2-methyl- and 2,3-dimethyl-but-2-ene to anisole. The effect of solvent on the mesa-cycloaddition of anisole and ethyl vinyl ether has not been observed in any other system and suggests the involvement of a polar species in the reaction pathway.

The photochemical reaction of benzene with ethylenes: studies with allyl compounds, enamines, vinyl sulphide, and 5,6-dichlorobicyclo[2.2.1]hept-2-ene

Benzene undergoes regio- and stereo-selective meta photocycloaddition to methyl but-3-enoate and pent-1-en-4-ol but methyl allyl ketone and NN-dimethylallylamine yield only products of the addend : likewise irradiation of benzene with enamines or methyl vinyl sulphide at 254 nm does not yield photoadducts. The meta photocycloadducts of benzene with methyl but-3-enoate and vinyl acetate and the ketones obtained by oxidation of the adducts from pent-1-en-4-ol are all essentially photostable and do not undergo Norrish Type II eliminations. The dechlorination products of the meta photocycloaddition of 5,6-trans-dichlorobicyclo[2.2.1]hept-2-ene and benzene undergo a retro-Diels-Alder addition at high temperatures, but the C8H8 isomer formed is cyclo-octatetraene.

Nucleic acid binding drugs. Part 12. X-Ray crystallographic and conformational studies on the anti-cancer drug m-AMSA and its mesyl derivative

The crystal structures of the anti-tumour agent m-AMSA [4′-(acridin-9-ylamino)-3′-methoxymethanesulphonanilide] and its mesyl derivative, as free bases, have been determined. They show a very distinct orientation of the substituted phenyl ring with respect to the acridine group, compared with m-AMSA hydrochloride (J. M. Karle, R. L. Cysyk, and I. L. Karle, Acta Crystallogr., 1980, B36, 3012). This has been rationalised in terms of intra- and inter-molecular interactions, the latter with ionic species in the salt crystal. Conformational calculations are also reported on these compounds, which indicate that they have interconvertible conformational flexibility.

The photo-cycloaddition of enol ethers to benzene

The photo-reactions of benzene with ethyl vinyl ether, n-butyl vinyl ether, 1,1 -dimethoxyethylene, 2,3-dihydropyran, 2,3-dihydrofuran, 2,3-dihydro-1,4-dioxin, and 1,3-dioxole are described. The meta-photo-cycloaddition of ethyl vinyl ether and n-butyl vinyl ether to benzene shows little selectivity, and regio- and stereo-isomers are isolated. ortho-Cycloaddition is observed from all systems but only with 2,3-dihydrofuran as addend are both stereoisomers of the adduct formed, and although the exo-isomer is very photolabile, the endo-product is essentially stable under its conditions of formation. The ortho-cycloaddition of 1,1 -dimethoxyethylene to benzene provides the first step in a convenient synthesis of cyclo-octatrienone. Contrary to previous proposals there is little correlation between the stereochemistry of the ortho-cycloaddition and preferred orientation of the addends in the ground state. The relationship between the relative efficiency of the two addition modes and ionisation potential of the ethylene is discussed.

Intramolecular photocycloaddition of phenethyl vinyl ether

Phenethyl vinyl ether has been shown to undergo photoisomerisation to the 1,3- and 1,4-intramolecular cycloadducts (3) and (4) in relative yields of 1 : 15 respectively.

Solvent effects in 1,3-photocycloaddition of vinyl ethers to monosubstituted benzenes

The photocycloadditions of vinyl ethers to benzonitrile, benzene, toluene, and anisole are described; the 1,3-cycloaddition of ethyl vinyl ether to anisole is unexpectedly promoted by polar solvents.