301. ChemInform Abstract: Photoadducts of 4,6-Dimethyl- and 4-Methoxy-6-methyl-2-pyrones with Chloroethylenes and Their Dehydrochlorination
- Author
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Otohiko Tsuge, Tetsuro Shimo, Kiyohisa Imada, Hisako Uemura, Kimiko Tanabe, Yusuke Wakikawa, and Kenichi Somekawa
- Subjects
chemistry.chemical_classification ,chemistry.chemical_compound ,Ethanol ,Double bond ,chemistry ,Group (periodic table) ,Benzene derivatives ,General Medicine ,Ring (chemistry) ,Hydrogen chloride ,Medicinal chemistry ,Triethylamine - Abstract
Sensitized photoreactions of 2-pyrones with chloroethylenes gave two kinds of [2+2]cycloadducts, 2-oxabicyclo[4.2.0]oct-4-en-3-ones (4, 8) and across the C3–C4 double bond in 2-pyrone, benzene derivatives, and/or cyclobutanecarboxylic acids: Their relative yields greatly depended upon the nature of the reactants. The dehydrochlorination of the cycloadducts 4 and 8 across the C5–C6 double bonds in the pyrones with triethylamine in ethanol gave 5-ethenyl-2-pyrones, whose structures were previously incorrectly assigned as oxocinones, via a symmetry-allowed ring opening of 2-oxabicyclo[4.2.0]octa-4,6-dien-3-ones. Some 5-ethenyl-2-pyrones possessing a chlorinated ethenyl group finally affords 5-ethynyl-2-pyrones by an anti-elimination of hydrogen chloride. The X-ray crystallographic analyses of 5-ethenyl- and 5-ethynyl-2-pyrones are also described.
- Published
- 1987
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