Organic & Biomolecular Chemistry 2008-08-21

Conformation and stereodynamics of 2,2'-disubstituted N,N'-diaryl ureas.

Jonathan Clayden, Loïc Lemiègre, Mark Pickworth, Lyn Jones

Index: Org. Biomol. Chem. 6(16) , 2908-13, (2008)

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Abstract

Except in the most hindered of cases, N,N'-diaryl N,N'-dimethyl ureas adopt a conformation with the two aryl rings disposed cis to one another. Variable temperature NMR studies reveal the rate at which the Ar-N bonds rotate as well as the conformational preference of ortho disubstituted ureas in which more than one cis orientation is possible. In general, a conformation in which the aryl rings lie close in space but with their most bulky 2-substituents aligned anti is preferred, but with particularly bulky 2-substituents, conformations in which one of the aryl rings points away from the other may also be populated.