Synthesis of Tetracyclo[6.2.2.23,6.02,7]tetradeca-4,9,11,13-Tetraene

The title hydrocarbon 3, a C₁₄H₁₄ tetracyclic tetraene of C_2v-symmetry, was synthesized by new routes starting from 1,8,9,10-tetrachloro-11,11-dimethoxytricyclo6.2.1.0^2,7]undeca-3,5,9-triene (1). The Diels-Alder cycloaddition of 1 with 2-chloroacrylyl chloride, a ketene equivalent, followed by subsequent reduction, dechlorination and deacctalization afforded the ketol 12 as a key intermediate. Elaboration of target compound 3 was carried out by either the method of ring enlargement of 12 or (better) the route of Diels-Alder reaction of decarbonylated 12 with trans-1,2-bis(phenylsulfonyl)ethcnc, an acetylene equivalent, to give trienol 17, followed by dehydration. Upon irradiation, 3 underwent intercyclic 2 + 2]-addition to caged hexacyclic diene 4. At 120°C, 3 decomposed into barrelene and benzene quantitatively.