Iron-catalyst Cross Dehydrogenative Coupling (CDC) Reaction

The transition metal coupling reaction is an effective synthesis strategy for the construction of C-C bonds and C-X bonds.From the classic cross-coupling reaction between carbon metal species and halogenated hydrocarbons,to the cross-coupling reaction based on the activation of C-H bonds,then to the cross-dehydrocoupling reaction between two different C-H bonds,towards the goal of developing more green,environmentally friendly and economical process.The emergence of cross-dehydrocoupling reactions has brought synthetic chemistry to a new platform.At the same time,iron,which is cheap and readily available,and environmentally friendly,is very attractive to chemists.We successfully realized the iron-catalyzed intramolecular CDC reaction of benzyl C（sp³）-H with aryl C（sp²）-H to the synthesis of 1-arylnaphthalene and 4-aryl coumarin compounds.The main findings are as follows:（1）We used 1,4-diphenylbutane as the template substrate and got optimized reaction conditions:2.5 mol%Fe Cl₃,5.0 eqiuv DDQ,DCE,N₂ atmosphere,100℃.Substrates with different substituent can obtain the target products in moderate to good yields.A fused-ring compound was obtained by using a symmetrical substrate containing a naphthalene ring.（2）Using phenoxypropylbenzene compounds as the reaction substrate,DDQ as the oxidant,Fe Cl₃ as the catalyst,and DCE as the solvent.Heat to 100℃under a N₂ atmosphere,and react for 36 hours.The raw materials were completely conversed,4-aryl coumarin compounds were obtained,and the product yield can reach up to 50%.When stoichiomefric TEMPO was added,no target product was detected.Therefore,the reaction should have experienced a radical process.Based on this,we proposed the corresponding reaction mechanism.