Ring of Rings

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Science  18 Mar 2011:
Vol. 331, Issue 6023, pp. 1366-1367
DOI: 10.1126/science.331.6023.1366-c

The abstract prospect of using a circle to derive a square has intrigued scholars of geometry for centuries. Segawa et al. have now used a square to derive a circle. The arena in this case was chemistry, rather than mathematics, and the task at hand was to assemble a molecular ring composed in turn of 12 benzene rings, linked to one another at the diametrically opposed 1 and 4 positions. Previous efforts had yielded small quantities of this [12]cycloparaphenylene in a mixture of variously sized relatives bearing 9 through 18 benzenes. The key to a more efficient route was a building block linking two benzene rings at an approximate right angle through an intervening cyclohexane diol derivative. By thoroughly optimizing a catalytic nickel system, the authors succeeded in linking four such building blocks in a single reaction medium to form a square with the cyclohexane rings at the corners and two benzenes along each edge. Dehydration/aromatization of the corner rings then honed the square into the circular targeted product in sufficient yield to afford a crystal structure.

Angew. Chem. Int. Ed. 50, 10.1002/anie.201007232 (2011).

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