Palladium-catalyzed Allylic C–H Oxidation

The investigation of oxidation,ammonification,sulfuration,fluorination,silanization and the C?C coupling of allylic substrates via the direct C?H bond activation are a hot field in contemporary organic chemistry.The strategy of C?H bond activation has highly atomic economy and step economy,which has potential and significant academic and industrial value.On the other hand,allylic C?H bond functionalization products,such as allylic alcohols,allylic esters and allylic ethers,are not only valuable chemical products,also commonly act as precursors of natural products.More and more chemists pay attention to this field and focus on allylic chemistry.In this paper,a series of allylic C?H bond functionalization catalyzed by palladium trifluoroacetate was studied.We used different nucleophiles,such as water,carboxylic acid,alcohol,carbazole,etc.The hydroxylation,esterification and etherification of the allyic C?H bond were successfully achieved.There are obvious advantages:（1）room temperature;（2）air atmosphere;（3）simple operation;（4）using readily available and inexpensive benzoquinones as oxidants;（5）high yield and regioselectivity.In addition,we found allylic trifluoroacetate intermediate during the course of reaction.We further executed two isotope labeling experiments by using H₂¹⁸O and stoichiometric metal mechanistic studies.On the basis of these studies,we proposed a tentative mechanism for our allylic C?H functionalization.At the same time,we carried out a gram level reaction and obtained the desired allylic alcohol with good yield,which implies its value in industry.