Palladium-Catalyzed Decarboxylative Selective Acylation of 4H-Benzo[d][1,3]oxazin-4-one Derivatives with α-Oxo Carboxylic acids via Preferential Cyclic Imine-N-Directed Aryl CH Activation

The benzoxazine scaffolds are of much interest as they are found in a large array of natural products and pharmaceutical drugs with diverse activities. We have developed a palladium‐catalyzed decarboxylative selective mono‐ and bis‐acylation of 4H‐benzo[d][1,3]oxazin‐4‐one derivatives with α‐oxo carboxylic acids via preferential cyclic imine‐N‐directed CH activation. 2‐Aryl‐4H‐benzo[d][1,3]oxazin‐4‐one was acylated with a variety of substituted phenylglyoxylic acids to produce the corresponding products. It was observed that electron‐donating groups (CH3, OCH3) at any position of the aromatic ring of phenylglyoxylic acid provided good to excellent yields, whereas phenylglyoxylic acids containing electron‐withdrawing groups (COCH3, CN, NO2) gave the products in moderate yields. Interestingly when the reaction was performed with silver triflate (AgOTf) in place of silver nitrate (AgNO3) in the presence of 4 equivalents of glyoxylic acid, the bis‐acylated product was obtained together with a small amount of mono‐acylated product. This is the first report of acylation of 2‐aryl‐4H‐benzo[d][1,3]oxazin‐4‐ones via CH activation. The notable features of this reaction are acylation with more challenging heteroarene‐oxo carboxylic acids and alkyl oxo carboxylic acids. This new protocol provides an easy and efficient access to a variety of o‐acyl‐4H‐benzo[d][1,3]oxazin‐4‐one derivatives which are of pharmaceutical importance.