Journal of the American Chemical Society 2008-11-05

Chiral squaramide derivatives are excellent hydrogen bond donor catalysts.

Jeremiah P Malerich, Koji Hagihara, Viresh H Rawal

Index: J. Am. Chem. Soc. 130(44) , 14416-7, (2008)

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Abstract

Thioureas represent the dominant platform for hydrogen bond promoted asymmetric catalysts. A large number of reactions, reported in scores of publications, have been successfully promoted by chiral thioureas. The present paper reports the use of squaramides as a highly effective new scaffold for the development of chiral hydrogen bond donor catalysts. Squaramide catalysts are very simple to prepare. The (-)-cinchonine modified squaramide (5), easily prepared through a two-step process from methyl squarate, was shown to be an effective catalyst, even at catalyst loadings as low as 0.1 mol%, for the conjugate addition reactions of 1,3-dicarbonyl compounds to beta-nitrostyrenes. The addition products were obtained in high yields and excellent enantioselectivities.