Intramolecular Cycloaddition Reactions of Dienyne Ethers. The Synthesis of Bridgehead Dienes and Their Thermal Rearrangements

Article abstract of DOI:10.1021/jo00237a019

The type 2 intramolecular Diels-Alder cycloaddition of dienyne ethers 13-16, 18, 19, and 22-25 have been surveyed in both gas and solution phase.The dienyne ethers undergo cycloaddition to yield a novel class of bridgehead dienes of general structure 4.The stability and mode of thermal reactivity of the resulting bridgehead dienes varies as a function of the tether length.Bridgehead diene 37 has a half-life of 7 h at room temperature in dilute solution.The homologous bridgehead dienes 28 and 40, although reactive molecules, are considerably more stable than 37.At elevated temperatures, bridgehead diene 37 rearranges to propellanes 35 and 36, while bridgehead diene 41 undergoes dehydrogenation to yield metacyclophane 42.All intramolecular Diels-Alder reactions are found to give a single regioisomeric cycloadduct.