An organocatalyst-mediated, asymmetric Mannich reaction in the presence of water without using organic solvents has been developed. A highly reactive siloxytetrazole hybrid catalyst has been developed for the reaction of dimethoxyacetaldehyde, while the sodium salt of siloxyproline is an effective catalyst of alpha-imino glyoxylate. Excellent enantioselectivity can be realized, and the usage of organic solvents can be reduced compared to the conventional reactions in organic solvents.

Direct and enantioselective: Diphenylprolinol silyl ether was found to catalyze the direct, asymmetric Michael reaction of 4-substituted 2-aryl-2-oxazoline-5-one and alpha,beta-unsaturated aldehydes, affording the chiral alpha,alpha-disubstituted alpha-amino acid derivatives with excellent enantioselectivity.

Enantioselective syntheses O 0031Organic Solvent-Free, Enantio-and Diastereoselective, Direct Mannich Reaction in the Presence of Water. -The siloxytetrazole hybrid catalysts are developed for the reaction of (I) with ketones and anisidine. The reaction of ethyl glyoxylate (V) with carbonyl compounds is also catalyzed by siloxyproline and its salts. -(HAYASHI*, Y.; URUSHIMA, T.; ARATAKE, S.; OKANO, T.; OBI, K.; Org. Lett. 10 (2008) 1, 21-24; Dep. Ind. Chem., Fac. Eng., Sci. Univ. Tokyo, Shinjuku, Tokyo 162, Japan; Eng.) -R. Steudel 23-024

Oxazole derivatives R 0220Diphenylprolinol Silyl Ether as a Catalyst in an Enantioselective, Catalytic Michael Reaction for the Formation of α,α-Disubstituted α-Amino Acid Derivatives. -Highly enantioselective Michael reaction of α,β-unsaturated aliphatic aldehydes (I) with oxazolidinone derivatives (II) is achieved in the presence of O-Tbs-diphenylprolinol as organocatalyst. Masked quaternary α-amino acid derivatives (III) are obtained in up to 99% e.e. and up to >90% d.e. The analogous reaction of aromatic α,β-unsaturated aldehydes is significantly less diastereoselective. -(HAYASHI*, Y.; OBI, K.; OHTA, Y.; OKAMURA, D.; ISHIKAWA, H.; Chem. Asian J. 4 (2009) 2, 246-249; Dep. Ind. Chem., Fac. Eng., Sci. Univ. Tokyo, Shinjuku, Tokyo 162, Japan; Eng.) -Mischke 22-123