Kartick C Bhowmick
University of Texas at San Antonio,
USA
Title: Small organic molecules as catalysts for asymmetric direct aldol reactions in aqueous media: A green chemistry approach for industrial applications
Biography
Biography: Kartick C Bhowmick
Abstract
Presently asymmetric organocatalysis in aqueous media is one of the most focused areas of research field in asymmetric synthesis. Asymmetric carbon-carbon bond forming reactions occupy the central area in the field of asymmetric organic synthesis where aldol reaction is the vastly studied one. A wide range of smart organic materials, including proline and its derivatives have been proved to be efficient catalysts for asymmetric aldol reactions. In recent years, more attention has been paid to develop organocatalysts for the asymmetric direct aldol reactions in water because it provides some unique properties, which include large cohesive energy density, very high surface tension, hydrophobic effect and most importantly it is environmentally benign solvent. The development of asymmetric organocatalyzed direct aldol reactions in aqueous media, for example, a very small organocatalyst, L-Proline hydrazide has been used for direct asymmetric aldol reaction of various ketones with aromatic aldehydes at room temperature in presence of several acid additives. A loading of 10 mol% of the catalyst and p-toluenesulphonic acid as additive was employed in this reaction, and good yields (up to 99%), with high anti/syn diastereoselectivities (up to 95:5) and enantioselectivities (up to >99.9%) could be achieved in aqueous media. Another new organocatalyst, derived from 4-hydroxy-L-proline and abietic acid was used for aldol reactions between substituted aromatic aldehydes and various ketones in presence of several acid additives in aqueous media. The corresponding aldol products were obtained in high isolated yields (up to 99%) with high anti-diastereoselectivities (up to 94%) and enantioselectivities (>99.9%). The catalyst loading was reduced to as low as 1 mol% only and very significantly, the aldol reactions were found to be extremely fast in water. In addition to the development of the above organocatalysts, the effect of several acid additives was investigated in asymmetric direct aldol reaction catalyzed by a C2-symmetric organocatalyst in aqueous media.