Theoretical Study On The Deacylation Reaction Mechanism Of α, α-diacetyl Cyclic Ketene Dithioacetal

In this thesis, quantum chemistry methods were used to investigate the deacylationreaction mechanism of α,α-diacetyl cyclic ketene dithioacetal, which is a kind of versatileintermediate in organic synthesis and has been widely studied in recent years.Protection and deprotection strategy are commonly used in the synthesis of naturalproducts and complex compounds. Carbonyl group is one of the most important organicfunctional groups. So far, thioacetalization is well-known as a reaction that protects carbonylgroups of aldehydes and/or ketones. The reagents of protecting carbonyl groups are mostlythiols. Though the reagents of thiols have lots of shortcomings: flammable, expensive,harmful, obnoxious odor, inconvenient transportation and stocking etc, because of thethioacetalization reaction is very important in organic synthesis, thiols are still widely adoptedas the reagents for protecting the carbonyl groups of aldehydes and/or ketones. Recently, Liuet al have succeeded in exploring a new kind of reagents instead of thiols: α,α-diacetyl cyclicketene dithioacetal, which is odorless solid and stable under ambient atmosphere. Thismethod of synthesis is simple, fast, high yield and mild condition. So these new reagents havegood perspective in the field of basic research and practical applications.With the rapid development of the computer technology and quantum chemistry,chemical simulations have gained much attention. Chemical simulations help us to understandmolecular behavior and to predict the properties of molecules involving molecular reactiondynamics. The study of the reaction mechanism and kinetics properties is a leading subject intheoretical chemistry. It is for the above reasons that much attention has been paid to thetheoretical research on these reactions.Our aim is to provide theoretical bases to reveal the reaction mechanisms of thedeacylation of the α,α-diacetyl cyclic ketene dithioacetal, involving the potential energysurface (PES), the dominant channels, stabilities and reactive of the reactants and products.According to the results of this work, we elucidate the mechanism that Bronsted acid,such as HCl, HBr, facilitates the deacylation reaction. Our calculation indicates thatpreferred pathways involving 1,2-addition and elimination mechanism and/or a moleculeaddition elimination mechanism. The calculated results are in good agreement with theexperimental fact that deacylation reaction of α,α-diacetyl cyclic ketene dithioacetal can bereached under room temperature.