Intramolecular cycloadditions of cyclobutadiene with dienes: experimental and computational studies of the competing (2 + 2) and (4 + 2) modes of reaction |
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Authors: | Limanto John Khuong Kelli S Houk K N Snapper Marc L |
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Institution: | Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, Massachusetts 02467, USA. |
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Abstract: | Highly functionalized, cyclobutene-containing adducts are afforded through intramolecular cycloadditions between cyclobutadiene and tethered dienes. The cycloaddition displays the following reactivity trend: cyclobutadiene serves as a dienophile in intramolecular reactions when it is connected to the diene through a four-atom tether. In cases where a three-atom linker separates the two reaction partners, the cyclobutadiene can function as both a diene and dienophile, affording a mixture of vinylcyclobutane (2 + 2) and cyclohexene-containing cycloadducts (4 + 2). Theoretical studies provide insight into the factors influencing the various pericyclic pathways operative in this system. In cases where cyclobutadiene functions as a diene to generate vinylcyclobutanes, these (2 + 2) adducts can be converted into the corresponding (4 + 2) cyclohexenyl products through a 3,3]-sigmatropic rearrangement. |
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