Synthesis of dichlorocyclobuta[b]benzofuran-2a-carboxylic derivatives and 3-(trichlorovinyl)coumarin through the cross photocycloadduct of coumarin and tetrachloroethylene
Synthesis of Dichlorocyclobuta[<i>b</i>]benzofuran-2a-carboxylic Derivatives and 3-(Trichloroethenyl)coumarin through Cross Photocycloadduct of Coumarin and Tetrachloroethylene
Photoirradiation of coumarin and tetrachloroethylene with a high-pressure mercury lamp through Pyrex filter in the presence of benzene and benzophenone gave cross cycloadduct (3) in a moderate yield. By treatment with bases or nucleophiles at room temperature, 3 underwent ring-contraction reaction through lactone-opening, cyclobutene formation, and intramolecular SN2′ displacement to yield dichlor