Generation, Isolation, and Characterization of a Stable Enol from Grignard Addition to a Bis-Ester: A Microscale Experiment for the Undergraduate Organic Chemistry Laboratory.

A microscale experiment for the undergraduate organic chemistry laboratory that consists of preparing and characterizing an α-ketoester and its corresponding, remarkably stable enol form, has been developed. The reaction is that of a Grignard reagent with a bis-ester. A difference in reaction temperature is responsible for the selective generation of the α-ketoester and the enol ester. Analysis of spectral data (1H NMR and IR) and a knowledge of organic reactions allows the students to determine the detailed structure of the two reaction products and also to suggest a mechanism for their formation. This experiment introduces students to the concept of stability of the tetrahedral intermediate in acyl-transfer reactions. It also gives them a taste of the unexpected.