DFT Studies On The Mechanism Of Pd-catalyzed Dearomatization Reaction

The functionalized alicyclic compounds are frequently found in natural products and bioactive compounds as important intermediates. The Pd-catalyzed dearomatization reaction is an effect method to synthesize functionalized alicyclic compounds. In addition, Pd-catalyzed dearomatization reaction has many advantages, for example, mild reaction condition, high output rate and without by-products. Therefore it has attracted considerable interest. Based on Gaussian, this article studies the mechanism of two kinds of Pd-catalyzed dearomatization reaction using DFT calculation.The first part is the Pd-catalyzed dearomatization reaction of chloromethynaphthalene with morpholine. Every step in catalytic cycle-oxidative addition, morpholine coordination, HCl elimination and -is investigated. In the whole reaction, the energy barriers of oxidative addition and reductive elimination respectively are 15.69 and 8.79 kcal/mol. Thus the oxidative addition is the rate-determining step. In oxidative addition and reductive elimination, we analyze the transition states by structure and NBO charge. We study the possible Stille product. The energy barrier is 24.47 kcal/mol, which is higher than that of dearomatization reaction by 8.78 kcal/mol. Thus this reaction is more feasible to produce dearomatization product. In addition, we perform a set of calculations in THF solution. The calculation shows that THF makes the energy barrier of the oxidative addition lower and makes the energy barrier of the reductive elimination higher. But the oxidative addition is still the rate-determining step. Therefore the solvent affect the energies of transition states and intermediates, but can’t change the general trend for the reaction potential energy surfaces.The second part is the Pd-catalyzed dearomatization reaction of naphthalene allyl chloride with allyltributylstannane. We study two kinds of possible mechanism about this reaction, and the pathway includes the cis-structure and trans-structure pathways starting from bis(η-ally)Pd complexes. In one mechanism, the bis(η3-ally) complexes are main intermediates and the energy barriers of cis-structure and trans-structure pathway are 44.28 and 53.73 kcal/mol, respectively. In the other mechanism, the (η1-ally1)(η3-ally1)Pd complexes are main intermediates and the energy barriers of cis-structure and trans-structure pathway are 18.68 and 24.21 kcal/mol, respectively. Therefore the second mechanism is more favorable kinetically and the c/s-structure pathway is more favorable than the trans-structure pathway. Two possible pathways to produce Stille coupling products are also examined. The energy barriers are 42.43 and 22.44 kcal/mol, which are higher than that of dearomatization reaction by 23.75 and 3.76 kcal/mol. Thus this reaction is more feasible to produce dearomatization product.