Azlactones (also known as oxazolones) are heterocycles usually employed in the stereoselective synthesis of α,α-amino acids, heterocycles and natural products. The versatility of the azlactone scaffold arises from the numerous reactive sites, allowing its application in a diversity of transformations. This review aims to cover classical and recent applications of oxazolones, especially those involving stereoselective processes. After a short introduction on their structures and intrinsic reactivities, dynamic kinetic resolution (DKR) processes as well as reactions involving stereoselective formation of a new σ C-C bond, such as alkylation/allylation/arylation, aldol, ene, Michael and Mannich reactions will be exposed. Additionally, cycloadditions, Steglich rearrangement and sulfenylation reactions will also be discussed. Recent developments of the well-known Erlenmeyer azlactones will be described. For the most examples, the proposed mechanism, activation modes and/or key reaction intermediates will be exposed to rationalize both the final product and the observed stereochemistry. Finally, this review gives an overview of the synthetic utility of oxazolones.

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An innovative method for the methylsulfenylation of electrophilic carbons was explored. Cheap and commercially available dimethyl sulfoxide (DMSO) was used as a source of the –SCH3 group. Chalcone, dibenzylideneacetone, and Morita–Baylis–Hillman adduct derivatives were successfully sulfenylated to give the corresponding products in moderate to high yields. Control experiments and DFT calculations revealed deoxygenation of DMSO and nucleophilic addition of a sulfur intermediate as key steps in the entire mechanism.