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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