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Cycloallenes, 9. — 1-Phenyl-1-aza-3,4-cyclohexadiene, the First Isodihydropyridine: Generation and Interception The generation of the title cycloallene 4 from 6,6-dibromo-3-phenyl-3-azabicyclo[3.1.0]hexane (10) with methyllithium according to the Doering-Moore-Skattebol method is reported. In the presence of styrene, 1,3-butadiene, furan, 1,3-cyclohexadiene, and 1,3-cyclopentadiene, 4 is intercepted in [2 + 2] and [4 + 2] cycloadditions with formation of the hexahydrocyclobuta[c]pyridines 6 and 11 and the hexahydroisoquinolines 12–15, respectively. The starting compound 10 is prepared via the cis-disubstituted 1,1-dibromocyclopropanes 8 and 9 from the known dioxepine derivative 7, the synthesis of which has been considerably improved. On treatment with n-butyllithium, the dichlorophenylazabicyclohexane 3 is converted into 4 as well. However, in the competition for 4, styrene is not successful against n-butyllithium, which transforms 4 into the pentadienylamine 5.