Total Syntheses of Angular [7]-, [8]-, and [9]Phenylene by Triple Cobalt-Catalyzed Cycloisomerization: Remarkably Flexible Heliphenes

✍ Scribed by Sangdon Han; D. Ryan Anderson; Andrew D. Bond; Hiufung V. Chu; Raymond L. Disch; Daniel Holmes; Jerome M. Schulman; Simon J. Teat; K. Peter C. Vollhardt; Glenn D. Whitener

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 129 KB
• Volume: 41
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/1521-3773(20020902)41:17<3227::aid-anie3227>3.0.co;2-t

✦ Synopsis

We have reported on the total syntheses of the first helical phenylenes (heliphenes), angular [6]-(1) and [7]phenylene (2), by a double cobalt-catalyzed cyclotrimerization strategy. [1] These hydrocarbons are the highest members of the, so far, five angular phenylene systems and, with 2, match the current size limit of all phenylenes. [2] Their properties are intriguing, including unusual mass spectrometric fragmentations for 1, a strongly attenuated bathochromic increment in the UV spectrum of 2, shielding of the terminal rings in 2 as a result of spatial overlap, alternating ring current intensities along the angular frame, X-ray crystallographic data that detail the helical and s-p distortive features, and, most surprisingly, an unusually low barrier for the enantiomerization of 2, which decreases on introduction of terminal substituents. To better understand these results, the construction of even higher members of the series was deemed imperative.

Here, we describe the total synthesis of angular [8]-(3 a) and [9]phenylene (4 a) [nucleus-independent chemical shift 1 5 -8.14 -3.12 -4.45 -4.06 -8.19 -2.95 -5.02