Photochemical Synthesis of Cyclopenta[c]-Anellated Benzopyrans and Benzothiopyrans

Abstract

On irradiation in the presence of 2,3-dimethylbut-2-ene the newly synthesized 2-oxo-2H-1-benzopyran- and 2-oxo-2H-1-benzothiopyran-4-carbonitriles are converted selectively to a cyclopenta[c]benzopyran or -thiobenzopyran, respectively. The reaction proceeds via addition of the alkene to the nitrile- and olefinic C-atoms of the triplet excited coumarin derivatives.

Key words

photochemistry - heterocycles - cycloadditions - nitriles - imines

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