1,4-naphthoquinone photocycloaddition

Photocycloaddition. Synthesis of the highly carcinogenic polycycHc hydrocarbons, eg (51) [72735-91-2] may be affected by photocycloaddition of 2-bromo-3-methoxy naphthoquinone [26037-61-6] with 1,1-diarylethylenes such as l,l-bis(p-methoxyphenyl)ethene (41). 

Strained cage compounds can be made by intramolecular photocycloaddition of properly designed ene/enone substrates. In an interesting example from J. R. Scheffer, a ben-zoquinone derived Diels-Alder product is regioselectively transformed into a (halO cage compound. This is a more complicated version of the classical intramolecular photochemical cyclization reactions of benzoquinone derivatives (for example see B. Pandey s cage synthesis from a naphthoquinone-cyclopentadiene in Chapter 3). 

Photocycloaddition of 2-methyl- and 2-ethyl-naphthoquinone to styrene yields three cyclobutane products (457,458) in which the 8-phenylisomer dominated. " The ratio of 7-phenyl to 8-phenyl products was 1 6 for the methylquinone and 1 3.5 for the ethyl derivative. The authors suggest that in these examples dipole-dipole interactions overcome any adverse repulsions. Changes in the olefin brings about changes in the ratio of products. Thus with 2-phenylpropene the ratio... 

The [ 2 + 2] photocycloaddition of 1,4-naphthoquinone to allyltrimethyl-silane has been described, and irradiation of 1,2-bis[trimethylsilyloxy]-... 

Ochiai and colleagues previously reported the 27i+2jt-photocy-cloaddition of the triplet excited state of 1,4-naphthoquinone with allyltrimethylsilane. Similar photocycloadditions of 2-trimethyl-silylcyclopentenone and 5-trimethylsilyluracil with alkenes have been discussed by Swenton and colleagues. - The photocycloadditions of allyltrimethylsilane to electron-deficient aromatic compounds via exciplexes have also been reported by other groups. " ... 

Sequential photocycloaddition of naphthoquinones (94) and (98), anthraquinone and phenanthrenequinone (101) with bicyclopropylidene (95) afforded [2 + 2] cycloadducts (96) and (99) and related polycyclic compounds including spirocyclopropanes. Photooxygenation of... 

Styrene derivatives are commonly used addends in the photocycloaddition studies of 1,4-quinones. With Z- and -anethole, 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and 9,10-anthraquinone in acetonitrile solvent yield spiro-oxetanes in which the trans-isomer (e.g., 4 from naphthoquinone) predominates. The process has been studied in detail by CIDNP techniques from which it is deduced that product formation proceeds from triplet radical ion pairs to the triplet biradical, and that there is no significant contribution from direct conversion of exciplex intermediates into the biradicals. Spiro-oxetane formation between simple alkenes and BQ generally has low regioselectivity but this is markedly improved with alkylidene cyclohexanes (Figure 87.3) such that the major isomer can be used as a new access to useful synthetic building blocks. For the BQ/homobenzvalene 5 system, however, where the difference in stability between the intermediate biradicals can be expected to be considerably less, the selectivity ratio for the spiro-oxetanes 6 and 7 is reduced to 3 1, respectively, and the addition to NQ yields only the cyclobutane derivative 8. Quadricyclane and norbornadiene undergo the same photocycloaddition reaction to BQ, affording the oxolane 9 and the spiro-oxetane 10. Evidence from CIDNP... 

Cleridou, S., Coveil, C., Gadhia, A., Gilbert, A., and Kamonnawin R, Photocycloaddition of arylethenes to 2-substituted-1,4-naphthoquinones and reactions of the cyclobutane adduct isomers,/. Chem. Soc., Perkin Trans. 1,1149, 2000. 

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