Kinetic and equilibrium study of the 2,3-furan ortho-quinodimethane - 4,5-dihydrocyclobuta(b)furan and 9,10-phenanthrene ortho-quinodimethane - 1,2-dihydrocyclobuta-(1)phenanthrene interconversions and related studies.

摘要

Preparation of 4,5-dihydrocyclobuta(b)furan (1) and 4-tert-butyl-4,5-dihydrocyclobuta(b)furan (2) was achieved by irradiation of 2,3-dimethylene-2,3-dihydrofuran (3) and 2-methylene-3-tert-butylmethylene-2,3-dihydrofuran (4), respectively. Compounds 1 and 2 were characterized by (sup 13)C NMR, (sup 1)H NMR, and IR spectroscopy. Kinetic analysis of the conversion of 1 to 3 (E(sub a) = 24.4 kcal/mol; log A = 10.1 s(sup (minus)1)), and 2 to 4 (E(sub a) = 28.0 kcal/mol; log A = 13.4 s(sup (minus)1)) was performed by (sup 1)H NMR in benzene-d(sub 6). The enthalpy difference between 1 and 3 and between 2 and 4 was investigated by pyrolyzing precursors to 3 and 4. Using a (Delta)S(degree) determined for the o-xylylene-benzocyclobutene interconversion it was determined that 1 was at least 4 kcal/mol less stable than 3 and that 2 was at least 5 kcal/mol less stable than 4. Preparation of 1,2-dihydrocyclobuta(1)phenanthrene (5) was achieved by irradiation of 9,10-phenanthrene o-quinodimethane (6) in solution in much higher yield than previously reported. Kinetic analysis of the conversion of 5 to 6 (E(sub a) 34.7 kcal/mol; log A = 13.2 s(sup (minus)1)) was performed using the method employed for 1 and 2. The interconversion between 6 and 5 was studied by the thermolysis of 5 in a dilute solution of benzene-d(sub 6) (K(sub eq) = 1) using (sup 1)H NMR analysis. The (Delta)H(sup 0) for 6 and 5 was calculated with the method used for the furan systems. Energy profiles for the interconversion between 6 and 5 and between o-xylylene and benzocyclobutene were compared, and differences were explained using Dewar Resonance Energies. Irradiation of 2-methyl-3-ethenylfuran led to an unsymmetrical dimer with one or possibly two acetyl groups. 9 tabs., 10 figs., 30 refs.