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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.
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Evolution of the Diels–Alder Reaction Mechanism since the 1930s: Woodward, Houk with Woodward, and the Influence of Computational Chemistry on Understanding Cycloadditions
Abstract This review article describes the evolution of Woodward's mechanistic thinking, beginning in the late 1930s and early 1940s with his proposal of a charge‐transfer mechanism for the Diels–Alder reaction, eventually leading to the Woodward–Katz two‐stage concerted mechanism in 1959, and then to its mechanistic solution in terms of orbital symmetry control. Houk′s research in the Woodward labs, testing the predictions of this theory, is described. Subsequent modern calculations with quantum mechanics and molecular dynamics simulations have shown that Woodward indeed had perfectly described not only the cyclopentadiene dimerization mechanism, but a new class of transition states now known as ambimodal or bis‐pericyclic transition states. In recent years, the Houk group has found that ambimodal reactions are operative in the [6+4] cycloaddition. Molecular dynamics simulations of many Diels–Alder and ambimodal cycloadditions provide a time‐resolved picture of how these reactions occur. Lastly, Roald Hoffmann provides a Coda in which he describes his joy in “being taken along the journey” of the cycloaddition story from Woodward's youth to today's trajectory simulations.
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- Award ID(s):
- 1764328
- PAR ID:
- 10231252
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 23
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 12660-12681
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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