Design of novel organocatalysts for asymmetric carbon-carbon bonds formation reactions

Abstract

In this project, a siloxy serine organocatalyst was developed for the asymmetric aldol reaction and Mannich reactions using either water or ionic liquids as the reaction medium. The synthesis of the organocatalyst using Z-protected serine amino acid was economical and operationally simple.

In chapter 2, the siloxy serine organocatalyst was shown to function as an efficient organocatalyst for the asymmetric aldol reaction using cyclic ketones as substrates in water. The direct aldol reaction between a selection of aromatic aldehydes and cyclohexanone resulted in good yields and high enantioselectivities (up to 98%) of anti-configured aldol products. In addition, the catalyst was also able to catalyze the preparation of syn-configured aldol products using TBDPSO-protected hydroxy acetone with a variety of aldehydes. The recyclability of this organocatalyst was also demonstrated using similar substrate scopes by extending the direct aldol reaction to the ionic liquid [bmim][BF4]. It is worth to note that the organocatalyst can be reused up to four times with comparable yields and selectivities (up to 92% ee). Comparable results were also obtained in the case TBDPSO-protected hydroxy acetone as the aldol donor.