The cover picture shows the molecular structure of the helically extended angular [8]phenylene. An unprecedented cobalt-catalyzed triple cyclization of an appropriate nonayne was successful in assembling the largest crystallographically characterized helical phenylene (heliphene). Its properties are intriguing; the heliphene is unusually configurationally labile and has a strongly attenuated bathochromic increment in the UV spectrum, shielding of the terminal rings as a result of spatial overlap, and alternating ring-current intensities along the angular frame. The X-ray crystallographic data detail the helical and s ± p distortive features. Most surprisingly, the remarkable flexibility of the heliphene provided an unusually low barrier (DG = (À 4.5 8C) 13.4 AE 0.4 kcal mol À1 ) for enantiomerization. The 1 H NMR spectrum was consistent with the alternation of cyclohexatrienoid and aromatic character; the terminal rings are the most diatropic and the penultimate ones the least. Further details about this chiral polycyclic benzenoid hydrocarbon are described by K. P. C. Vollhardt, et al. on p 3227 ff.

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Sechs der Cyclobutadienringe im gewinkelten [8]Phenylen und [9]Phenylen 1 entstehen bei der neuartigen Cobalt‐katalysierten dreifachen Cyclisierung geeigneter Nonaine. Diese gespannten Produkte sind die größten bekannten Phenylene und konfigurativ ungewöhnlich labil. Ihre Synthese ermöglichte eine erste Abschätzung der Eigenschaften des hypothetischen Polyheliphens.

3-Mercapto-2(1H)-pyridinone (1) can be synthesized in three simple high-yielding steps from readily available 2-tert-butylthiazolo[4,5-b]pyridine (2). Its disodium salt condenses with o-chloronitrobenzene, 2-chloro-3-nitropyridine, and 3-chloro-4-nitropyridine 1-oxide to give respectively 4-azaphenoxathiine (10), 1,6-diazaphenoxathiine (12), and 2,6-diazaphenoxathiine 2-oxide (14) which reduces to 2,6-diazaphenoxathiine (15). The structures of these previously unreported azaphenoxathiine systems were confirmed by assignment of their respective (13)C NMR spectra.