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Catalytic Generation of Vinylthionium Ions. (4 + 3)-Cycloadditions and Friedel–Crafts Alkylations

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journal contribution
posted on 05.09.2014, 00:00 by Michael Topinka, Rama Rao Tata, Michael Harmata
A 3-phenylsulfanyl-substituted allylic alcohol and an ester thereof were treated with Brønsted acids or a gold catalyst, respectively, to generate vinylthionium ions. These species react with dienes, primarily substituted furans, to give products of either (4 + 3)-cycloaddition or Friedel–Crafts alkylation. The results are rationalized on the basis of a stepwise mechanism in which the relative rates of ring closure versus proton loss in the intermediate σ-complex determine the course of the reaction.