Photocycloaddition of 2,3-Dihydro-2,2-dimethyl-4H-thiopyran-4-one (a 4-Thiacyclohex-2-enone) to bona fide Triplet Quenchers. A Contradiction?

Abstract

2,3-Dihydro-2,2-dimethyl-4H-thiopyran-4-one undergoes regiospecific photocycloaddition to 2-chloroacrylonitrile as well as regio- and stereospecific photocycloaddition to ethylidenemalononitrile. On irradiation in the presence of either 2,3-di­methylbuta-1,3-diene or isoprene, the same enone affords mainly [2+2]-cycloadducts and only minor amounts of (stepwise) [2+4]-cycloadducts, whereas quantitative quenching is observed in the presence of 2,5-dimethylhexa-2,4-diene. In contrast, the corresponding pyran is almost quantitatively quenched in the presence of any of the enenitriles or dienes mentioned.

Key words

[2+2] photocycloaddition - 1-chlorocyclobutanecarbonitriles - vinylcyclobutanes - 1,4-biradicals

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CCDC-633282 contains the supplementary crystallographic data for 5. This data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request.cif.

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CCDC-632623 contains the supplementary crystallographic data for 10. This data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request.cif.