Preparation and thermolysis of exo-and endo-Tricyclo[6,2,1,02,7] undeca-3,5,9-triene

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Abstract
Syntheses of exo- and endo-tricyclo[6,2,1,02,7]undeca-3,5,9-triene, (3) and (4) respectively, are described. Both trienes undergo ready π4s+ π28 cycloreversion to yield cyclopentadiene and benzene at 40-60�C, the exo-triene (3) being slightly more reactive. At 60�C, for (3) k = 2.29x 10-3 s-1, ΔH? = 104.1 � 4.2kJ mol-1, ΔS? =14.6 � 1.6 mol-1 K-1, while for (4) k = 5.25 x 10-3s-1, ΔH? =ll5.0 � 3.3 kJ mol-1, ΔS? = 34.3 � 13.0 J mol-1 K-1 .� The cycloreversion of (3) and (4) are believed to be concerted reactions. The related dienes exo- and endo-tricyclo[6,2,1,02,7]undeca-3,5-diene, (25) and (28) respectively, have also been prepared, and are stable up to 200�C. At 300�C, interconversion between (25) and (28) occurs, apparently via bicyclo[6,2,1]undeca-2,4,6-triene. The relationship of the trienes (3) and (4) to the recently described bicyclo[6,2,l]undeca-2,4,6,9-tetraene is discussed.

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