The syntheses of several topological forms of the phenylenes have been reported, [1] but an exploration of their chemical behavior has been limited mainly to the parent system [2]phenylene (biphenylene), [2] the linear frame (e.g. the linear [3]phenylene 1), [3] and the triangular variety (e.g. the C 3 -symmetric [4]phenylene 2).[4] Noticeably absent from these investigations is the behavior of angular [3]phenylene (3), for which only hydrogenation of the central ring [4a, 5] and flash-pyrolytic isomerization have been recorded. [6] In 3, angular fusion minimizes cyclobutadienoid antiaromaticity by rendering the central ring extensively (62 %) bond-localized and thus comparatively less diatropic, [4a, 7] while leaving one double bond exposed. In contrast, and besides its distinct topology, 1 is qualitatively very different [1a, 3] with a distorted but relatively more diatropic center, flanked by relatively paratropic neighbors. [7] On the other hand, 2 differs quantitatively in the degree of central cyclohexatriene character (100 %) and exhibits lower steric

The syntheses of several topological forms of the phenylenes have been reported, [1] but an exploration of their chemical behavior has been limited mainly to the parent system [2]phenylene (biphenylene), [2] the linear frame (e.g. the linear [3]phenylene 1), [3] and the triangular variety (e.g. the C 3 -symmetric [4]phenylene 2).[4] Noticeably absent from these investigations is the behavior of angular [3]phenylene (3), for which only hydrogenation of the central ring [4a, 5] and flash-pyrolytic isomerization have been recorded. [6] In 3, angular fusion minimizes cyclobutadienoid antiaromaticity by rendering the central ring extensively (62 %) bond-localized and thus comparatively less diatropic, [4a, 7] while leaving one double bond exposed. In contrast, and besides its distinct topology, 1 is qualitatively very different [1a, 3] with a distorted but relatively more diatropic center, flanked by relatively paratropic neighbors. [7] On the other hand, 2 differs quantitatively in the degree of central cyclohexatriene character (100 %) and exhibits lower steric

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