| Popis: |
A [5,5]sigmatropic rearrangement never previously observed with a carbon skeleton was discovered during attempts to develop a new and versatile access to 3,8-disubstituted heptalenes as building blocks for the still unknown parent heptalenophanes. Dimethyl 5,5a,10,10a-tetrahydroheptalene-3,8-dicarboxylate (8), easily synthesized from cis-bicyclo[3.3.0]octane-3,7-dione (4), rearranges even below 0°C to the isomeric 1,6-dicarboxylate 9, which can be transformed into 1,6-dimethylheptalene. Measurement of the kinetic and thermodynamic parameters of the rearrangement of derivatives of 8, together with studies on the influence of substituents and semiempirical AM1 calculations, gave information on the mechanism of the pericyclic reaction. |
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