Evaluation of L – Proline as a Catalyst for an Asymmetric Aldol Reaction

Abstract
This reaction is divided into two parts. In the first part acetone, L – proline and 4 – nitrobenzaldehyde are reacted to give (R)-4-hydroxy-4-(4-nitrophenyl)butan-2-one as the major product along with (S)-4-hydroxy-4-(4-nitrophenyl)butan-2-one. The identity of the product is confirmed by IR spectra of the product which gives peaks at 1073.94 cm-1, 1330 cm-1, 1515.05, 1600.13 cm-1, 1708.25 cm-1, 2930.82 cm-1and broad peak at 3418.10 cm-1. The mass of the product is 0.013 grams which gives a percentage yield of 29.81%. The melting point of the product is not taken due to minimal product.
In the second part of the reaction excess reagents are used and the synthesized product is in very small quantities. The product synthesized is diastereomers of 1-(4-nitrophenyl)-3-oxobutyl 3,3,3-trifluoro-2-methoxy-2-phenylpropanoate. The identity of this compound is confirmed by the following peaks seen in 1H NMR: 8.19 and 7.62 ppm, 5.47 ppm, 2.90, 2.13 ppm, 3.30 ppm, 7.36 – 7.38 ppm. The melting point, IR spectrum, theoretical yield or percentage yield is not found since all of it used in 1H NMR analysis. The product 1H NMR shows a mix of both the diastereomers, but it is difficult to ascertain which one is in excess.
Introduction
The aldol reaction that was experienced in this lab is the nucleophillic addition of an enolate to a carbonyl group to form a B-hydroxycarbonyl. This reaction is a very powerful method to construct of carbon-carbon bonds. Nature has developed the aldolase enzymes that catalyze biological aldol reactions. Aldolase is the enzyme that produces only one enantiomeric product that is hard to achieve. A simple amino acid L-proline can be used as the aldolase catalyst in asymmetric aldol reaction of acetone with a variety of aldehydes. This method produced 68% and 76% of