Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity

Angew Chem Int Ed Engl. 2018 Jul 26;57(31):9901-9905. doi: 10.1002/anie.201803872. Epub 2018 Jul 4.

Abstract

The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels-Alder trapping of the BCB by either pendant or external electron-deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three-component process joining the benzyne first with an electron-rich and then with an electron-poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4π diene component in Diels-Alder reactions are reported. The results also shed new light on aspects of the hexadehydro-Diels-Alder reaction used to generate the benzynes.

Keywords: alkyne cascade reactions; arynes; benzocyclobutadienes; cyclization; cycloaddition.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alkynes / chemistry*
  • Cycloaddition Reaction
  • Cyclobutanes / chemical synthesis*
  • Cyclobutanes / chemistry
  • Density Functional Theory
  • Molecular Structure

Substances

  • Alkynes
  • Cyclobutanes
  • benzocyclobutadiene