Enol Nitrosation Revisited: Determining Reactivity of Ambident Nucleophiles

Luis García-Río, Juan C. Mejuto, Mercedes Parajó, and Moisés Pérez-Lorenzo

Eur. J. Org. Chem., 2009, 26, 4525–4533

Enols are one of the most important types of ambident nucleophiles being widely used as reagents in organic chemistry. The relevance of enols has led to considerable interest in developing methods to determine the reactivity of their nucleophilic centers. In this sense, the mainstream literature works on this topic make use of a combination of overall rate constants together with the analysis of the reaction products. By knowing the product ratio it is possible to determine the ratio between the reaction rates on each site. Thus, the reactivity for each nucleophilic position can be obtained. This is a reliable approach as long as the isolation or in situ characterization of the reaction products can be carried out. In the case of unstable and/or interconvertible products where the use of identification techniques is not possible, an alternative methodology must be found. For that reason, our research group has developed a model that allows us to study and quantify separately the reaction rates of enol nucleophilic centers even if only one final reaction product is obtained. This model is based on the fact that nitrosation of enols shows well-differentiated behavior depending on whether the reaction proceeds through the carbon or the oxygen atom. The present study provides insights into the ambident nature of enols as well as a methodology for determining the chemical reactivity of their nucleophilic centers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)