Summary: | The cycloaddition of allylic cations to conjugated dienes forming a seven-membered ring is a logical extension of the Diels-Alder reaction. The first clear-cut examples of this reaction are reported in this thesis. The 2-methylallyl cation can be generated from the iodide with a silver salt in the presence of a diene. With cyclopentadiene and silver trichoracetate the product include 3-methylbicyclo(3,2,1)octa-2,6-diene, 3-methylenebicyclo(3,2,1) oct-6-ene, and exo-and-endo 3-methylbicyclo(3,2,1) oct-6-ene, and exo and endo-3-methylbicyclo(3,2,1) oct-6-en-3-yl trichloracetates. Cyclohexadiene forms 3-methyl-bicyclo (3,2,2) nona-2,6-diene, but with furan the product is 2-(2-methylallyl)furan. The transition state for the reaction is shown to have a preference for a chair like structure. Evidence for this is provided by the formation of N)exo-3-methylbicyclo-(3,2,1)oct-6-en-3-yl)acetamide as the only epimer when acetonitrile is present as nucleophile. The role of the solvent is discussed and it is suggested that liquid sulphur dioxide and benzene have a stabilizing influence on allylic cation.
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