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.
Bibliographical noteFunding Information:
This work was supported by the U.S. Dept. of Health and Human Services [National Institute of General Medical Sciences (R01 GM65597, then R35 GM127097)] and the National Science Foundation (CHE-1665389). Computational work was made possible by the University of Minnesota Supercomputing Institute (MSI). Some of the NMR data were obtained with an instrument funded by the NIH Shared Instrumentation Grant program (S10OD011952). We thank Victor G. Young, Jr. (University of Minnesota) for the X-ray diffraction analysis.
© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
- alkyne cascade reactions