Two-Phase Oxidation of Sulfoxonium Ylides with Oxone: A Green Route to the Synthesis of α-Keto Aldehydes.

α-Keto aldehydes are flexible and versatile synthetic building blocks widely used for constructing heterocyclic systems. However, classical methods for synthesizing α-keto aldehydes, based on the oxidation of the corresponding methyl ketones, cannot be employed for the synthesis of α- monosubstituted benzylglyoxals. The only method described so far for obtaining such α-keto aldehydes has been a multi-step transformation of synthetically challenging α-cyano-α-hydroxymethyl epoxides. This article describes a new, simple, and safe transformation based on the oxidation of readily available sulfoxonium ylides under the action of Oxone. The reaction is carried out in a biphasic water-organic solvent system, which greatly simplifies the isolation process. Short-path distillation of the obtained oligomers provides a wide range of α-keto aldehydes.