Peter Heath

Substituent effects on the intramolecular photochemical reactions of phenyl–ethenyl non-conjugated bichromophoric systems

The effects of substitution on the photochemistry of phenyl–ethenyl bichromophoric systems are reported. Methyl substitution at the 2-, 3-, 5-, and 1,1,2-positions in the pentene moiety of 5-phenylpent-1-ene reduces both reaction efficiency and selectivity but in contrast to intermolecular analogues the photoreaction of 3-phenethylcyclohexene is comparable with that of the corresponding cyclopentene. Incorporation of ester units in the connecting unit between the chromophores or on the ethene inhibits intramolecular cyclisation as does the presence of para OMe, CN, or COMe groups in 5-phenylpent-1-ene. In contrast reaction selectivity and efficiency are greatly promoted by ortho Me or OMe groups and the products reflect exclusive 1,3-cycloaddition. The presence of a para Me group in 5-phenylpent-1-ene leads to specific 2,6-intramolecular cyclisation but the reaction of the meta-Me derivative leads to four products derived from 1,3- and 1,5-intramolecular cycloaddition. The observations are discussed in terms of mechanisms of arene–ethene photoreactions and preferred conformations of the bichromophores.

Intramolecular meta photocycloaddition of 3-benzyl(dimethylsila)prop-1-enes

Abstract The regiochemistry of intramolecular meta photocycloaddition of 3-benzyl(dimethylsila)prop-1-enes is controlled by the silicon in the tether and the presence of an electron donor substituent on the phenyl ring. For 1′,3′-addition, the preferred formation of the angular rather than the linear triquinane isomer is interpreted in terms of an asymmetric orientation of the S 0 ethene and S 1 benzene inducing a non-synchronous addition which then promotes specific 2′,4′-cyclisation to give the cyclopropane ring of the dihydrosemibullvalene skeleton.

Photocycloaddition of ethenes to cyanoanisoles

Abstract The photoreactions of 2-,3-, and 4-cyanoanisole with cis cyclo-octene, ethyl vinyl ether and acrylonitrile have been investigated. Additions of the cyclo-alkene reflect control of the reaction by the methoxy group to give predominantly meta cycloadducts by 2,6-attack. In contrast these arenes and ethyl vinyl ether undergo ortho cycloaddition which in the case of the product from the 2-arene isomer, leads to a convenient high yield synthesis of the bicyclo[4.2.0]octa-2,7-diene (23). The reactions of acrylonitrile with 2- and 3-cyanoanisoles are slow and non-selective but ortho cycloadducts are formed from the 4-isomer which also undergoes novel photoaddition with the cyano group of both acrylonitrile and benzonitrile to give azacyclo-octatetraenes.

Specific ortho photocycloaddition of enol ethers to 2-substituted anisoles: Facile synthesis of bicyclo[4.2.0]octa-2,7-dienes in sunlight

Abstract Enol ethers undergo specific ortho photocycloaddition to anisoles which have electron withdrawing substituents in the 2-position to give good yields of bicyclo[4.2.0]octa-2,7-dienes as the photostable products.

The preparation of dioxaprostacyclin analogues from D-(—)-ribose

Using D-(—)-ribose as chiral starting material, we have prepared 1-deoxy-D-ribofuranose by a novel route, and then employed both compounds as precursors of the dioxaprostacyclin analogues (2).

Steric effects in the meta photocycloaddition of ethylenes to alkylbenzenes

Abstract Vinyl acetate and cis cyclo-octene undergo regioselective meta photocycloaddition to alkylbenzenes: the orientation of attack suggests that adduct formation can occur by two different mechanisms.

Inter-and intra-molecular photocycloaddition of enol ethers to naphthalene

The isomeric non-conjugated naphthyl enol ether bichromophores (6) and (7) display markedly different photoreactivities. The former undergoes [2π+ 2π] cycloaddition from the S1 state whereas the latter is relatively photostable. The two cyano derivatives (4) and (5) both yield intramolecular cycloadducts but the orientation of the addition is the opposite of that predicted from the reported intermolecular cyanonaphthalene–enol ether photoreactions. 2,3-Dihydrofuran undergoes specific ‘head to head’endo photoaddition to naphthalene but in contrast the major adducts from 2,3-dihydrofuran and this arene have ‘head to head’exo and ‘head to tail’endo structures. The adduct (18) undergoes a facile 1,3-shift to yield the (4π+ 2π)endo adduct (19). The reactivities of the bichromophores and the regiochemistries of the additions are considered in relation to the relative charge densities at the 1- and 2-positions of the S1 arene.

The synthesis and spectroscopic characterization of bis(γ-methoxypropyl) cadmium

Abstract The preparation of the hitherto-unknown compound (CH 3 O(CH 2 ) 3 ) 2 Cd is reported. It is a colourless oil, which has been shown by mass spectrometry to vaporize without decomposition. A thorough vibrational and multinuclear magnetic resonance study suggests strongly that there is no internal coordination of the O atoms to the Cd atom, whereas such coordination is observed in the zinc-containing analogue.

Isolation of 1-tert-butyl-1, 4-dihydro[60]fullerene, and its base-catalysed rearrangement to the 1, 2-dihydro[60]fullerene analogue

Abstract Reaction of tert-butyllithium with [60]fullerene followed by acid quench affords the 1-tert-butyl-1, 4-dihydrofullerene, which can be isolated substantially pure. The solid material appears to be indefinitely stable, but in solution undergoes base-catalysed rearrangement to the 1, 2-isomer. The kinetics and energy of activation for this rearrangement are presented.

Proton migration on the [60]fullerene cage of1-tert-butyl-1,4-dihydro[60]fullerene to yield the1,2-isomer

Proton NMR data on the base catalysed rearrangement of 1-tert-butyl-1,4-dihydro[60]fullerene to the 1,2-isomer reveal a second order reaction and an activation energy of 56.1 kJ mol - 1 .