Density Functional Theory Study Of The Diels-Alder Reaction In The Synthesis Of Abietane Diterpenes

The transannular Diels-Alder (TADA) reaction is unparelleled in its ability to generate high degree of stereochemical and architectural complexity in a single tranformation,which has been pay attention by people to it is important role in the synthesis of many terpene natural products. In the past few years,the TADA reaction has emerged as powerful tool to approach polycyclic diterpenes having various special pharmacological activities including antitumor, by changing groups and number of atoms.In recent years,the hetero Diels-Alder reaction has emerged as an elegant protocol for the construction of six membered heterocyclic system,especially natural products.Density Functional Theory(DFT), at the B3LYP/6-311G(d,p)level of theory and Moller-Plesse Theory (MP2/6-311G(d,p) has been performed to study the mechanism, potentiall energy surface of the Diels-Alder reactions.The main results and conclusions are as follows:(1) Diels-Alder reactions in the Synthesis of abietane diterpenes:the obtained results indicate that the reactions are concerted and synchronous processes and interpreted with Frontier Orbital Theory, which are in full agreement with results both thermodynamically and kinetically. All transannular products are formed via a six-member ring transition state, yield of the endo products is higher. And finally, the enthalpies and activation energies of all the reactions are given respectively, in the Synthesis of abietane diterpenes Reaction2is not easy.The reactions are exothermic,which accord well with experimental observations.(2) Hydrogen-mediated carbon-sulfur bond formation is prior to carbon-carbon bond formation in hetero Diels-Alder reactions.The reactions are concerted and nonsynchronous processes and interpreted with Frontier Orbital Theory, which are in full agreement with results both thermodynamically and kinetically. The principal stream of electrons flows. from High Occupied Molecular Orbital(HOMO) orbital of diene to Lowest Unoccupied Molecular Orbital of Dienophile.Because of steric hindranceof ethyl and diene with electron-donating group, system3-2reacts easily.Reaction3-1is is an endothermic reaction and Reaction3-6,3-11,3-16are exothermic Reactions.(3) The obtained results indicate that the reactions are concerted and synchronous processes in synthesis of substituted3-furan-2(5H)-ones via an anthracene Diels-Alder sequence. R2#is parallel approach to R1#,orbits reaching maximal overlapping sequence, which are in full agreement with results both thermodynamically and kinetically. All reactions are exothermic Reactions, which accord well with experimental observations. (4) The reactions are concerted and nonsynchronous processes in novel chiral1-phosphono-1,3-butadiene for asymmetric hetero Diels-Alder cycloadditions with nitroso and azodicarboxylate dienophiles. Oxygen electric negative outweiqhs Nitrogen electric negative, and the existence of methyl of Nitrogen, carbon-oxygen bond formation is prior to carbon-nitrogen bond formation. The reaction is exothermic Reactions,△H1is-108.77742kJ·mol-1,which accords well with experimental observations.