Abstract
AbstractThe cycloadditions of the titled two masked o‐benzoquinones, 2 and 3, with monosubstituted ethylenes including ethyl acrylate, styrene, ethyl vinyl ether and 1‐hexene were studied. The reactions proceeded with high stereoselectivity and regioselectivity to give endo head‐to‐head adducts when ethyl acrylate, styrene and ethyl vinyl ether were used as addenda. In the case of 1‐hexene, the reaction with 2 took place with high regioselectivity but low stereoselectivity to afford endo as well as exo head‐to‐head adducts while the reaction with 3 occurred with less regioselectivity to produce presumably all the eight possible isomers. The regiochemistry of the adducts were determined by the 1H nmr analysis of their hydrolysis products, bicyclo[2,2,2]oct‐5‐en‐2,3‐diones 6, and the subsequent photolysis products, 1,3‐cyclohexadienes 7. The stereochemistry was established by the study of the lanthanide induced shifts of compounds 6a‐6f with Fu(fod)3. The regioselectivity and stereoselectivity of these cycloaddition reactions were explained in terms of frontier molecular orbital theory and steric effect. The present study provides also a facile method to prepare regioselectively bicyclo[2, 2, 2]oct‐5‐en‐2,3‐diones (stereo‐selectively also) and 1,3‐cyclohexadienes from unsymmetric catechols via masked o‐benzoquinones.
Published Version
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