Structure of biaryls. Atropisomerism

Moreover, the biaryls substituted in the orf/zo-positions which are too hindered to rotate, under the standard conditions, mainly tetra-orf/zo-, but also tri- and, in some cases of extreme encumbered ort/zo-substituents, even di-substituted biaryl, can be principally resolved into the two isomeric forms named atropisomers [7]. 

However, the direct assignment of the absolute configuration at the biaryl axis is achieved by the measurement of a circular dichrolsm (CD) and the X-ray determination of crystal structure [7], 

During more than a hundered years since the first biphenyls were obtained by synthetic methods, several excellent rewievs on this topic have appeared. Many of them were used during the preparation of this book and are cited throughout discussion in the following Chapters. Herein, two valuable rewievs are noteworthy [8,9], First, published in 2002 by Lemaire s group [8], is the most detailed and extremely useful overwiev of all relevant aryl-aryl bond forming reactions. The second one, also excellently presented, focused mainly on the natural products synthetic problems and chiral biaryls, was written by Brlngmann and his coworkers [9]. 

Wilen and L. N. Mander, Stereochemistry of Organic Compounds, John Wiley Sons, Inc., New York, 1994. 

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