Chloranil, photocycloaddition with

Chloranil, photocycloaddition with butadiene, 474 Chlorophylls, 552 Chu, N. Y. C 439 Ciamician, G., 1, 2,459 Cinnamic acid, solid state photodimerization, 476... 

Photocycloaddition of aromatic carbonyl compoimds with p,p-dimethylketene silylacetals gave 2-alkoxy-4-aryloxetanes <98JCS(P1)3253>. A similar photoaddition of derivatives of stilbene to chloranil gave the isomeric spiro oxetanes 16 in very high total yields <99JOC2250>. 

An extensive review of 2 + 2-photocycloadditions of dienones and quinones has been published. The photocycloaddition of heterocyclic 2,3-diones (18) with electron-rich alkenes in the presence of the photosensitizer benzophenone yields 2-1-2-cycloadducts (19) and (20) with high regio- and stereo-selectivity (Scheme 1) Time-resolved spectroscopy has shown that in the photochemical cycloaddition between stilbenes and quinones, the (singlet) ion-radical pair [S ", Q+ ] is the primary reaction intermediate and therefore establishes the electron-transfer pathway for this typical Paterno-Biichi transformation. A kinetic study of the Paterno-Biichi cycloaddition of stilbene to chloranil shows that solvent polarity and donicity control the formation as well as the reaction path of the ion-radical. The photoirradiation of chloranil with... 

Braun, M., Christl, M., Peters, E.M., and Peters, K., Photochemical reactions of chloranil with norbornene, bicyclo[2.1.1]hex-2-ene and cyclopentene. A novel intermolecular photocycloaddition,/. Chem. Soc., Perkin Trans. 1, 2813, 1999. 

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