The synthesis and thermal rearrangement of 2,5-Dialkyl-1,3,4- triphenyl-2,4-cyclopentadien-1-o1's

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Virginia Polytechnic Institute and State University


Three 2, 5-dialkyl-1, 3, 4-triphenyl-2, 4-cyclopentadien-1-ols and 2, 5-di(t-butyl)-1, 3-diphenyl-2, 4-cyclopentadien-1-ol were prepared from their precursor ketones using phenyllithium and Grignard reagent. In general, the phenyllithium reagent produced products faster and in better yield and purity than the Grignard reagent. The alcohols were rearranged thermally to obtain the appropriate ketones and to obtain information about the relative rates of the rearrangement. The rearrangement of the three 2, 5-dialkyl-1, 3, 4-triphenyl-2, 4-cyclopentadien-1-ols were studied kinetically and the results compared with those obtained from similar studies on 1,2,3,4,5-pentaphenyl-2,4-cyclopentadien-1-ol. The alcohols all possessed energies of activation and enthalpies of activation which were essentially identical, these supporting earlier theory that no linear free energy relationship (LFER) exists in these rearrangements and that a purely concerted mechanism exists in these cases. The rate of reaction for 15,16,17—triphenylbicyclo[12.2.1] heptadeca-14,16-dien-1-ol was very much faster than any other studied alcohol. The difference in this rate is thought to be due to the severe steric restraints that are present in this alcohol. The entropy of activation for this strained alcohol was shown. to be much less than for the other alcohols.