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Synfacts 2011(4): 0439-0439  
DOI: 10.1055/s-0030-1259618
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart ˙ New York

Internal Lewis Acid Activation of Ureas

Contributor(s): Benjamin List, Lars Ratjen
S. S. So, J. A. Burkett, A. E. Mattson*
The Ohio State University, Columbus, USA
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Publication History

Publication Date:
18 March 2011 (online)

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Significance

The authors reported the synthesis and application of boronate ureas, such as 1, for the activation of nitrostyrenes towards indole ­additions. With this type of catalyst in hand, an up to ten-fold rate enhancement compared to Schreiner-type ureas was observed (see for example: P. R. Schreiner, A. Wittkopp Org. Lett. 2002, 4, 217). The high activity results from a strong Lewis acid mediated acidification of the urea functionality. However, it was also demonstrated that further pK a enhancement by additional electron-withdrawing substitution in the same benzene ring is counterproductive.