“Perhaps” is the answer to the question posed in the title. What is heating cyanoacetylene 1 to 160 °C in benzene leads to intermediates (2 a, b) that behave like cyclobutadiene-l, 2-dicarbonitrile. This has now been demon strated in the presence of the trapping reagent [2.2]paracyclophane, resulting in the Diels-Alder adducts of 2 a and 2b.
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