Synthesis Of Functionalized Benzofurans Based On New C-C Coupling Reactions At The α Position Of Ketene Dithioacetals

α-Oxo ketene dithioacetals are versatile intermediates in organic synthesis, and have avarity of chemical properties owing to their structural diversity.-Oxo ketene dithioacetalshave been widely applied to the construction of different kinds of poly stubstituted carbo-andheterocylic compounds. During a hundred years of development, exspecially in the past thirtyyears, the chemistry of α-oxo ketene dithioacetals has become an important research topic inorganic chemistry.In the structure of α-oxo ketene dithioacetals, the carbon-carbon double bond is highlypolarized due to the push-pull interreaction of the electron-withdrawing carbonyl group andelectron-donaying dialkylthio groups. Thus, the-carbon atom of a-oxo ketene dithioacetalis potentially a nucleophilic center, can react with a wide variety of electrophiles. As animportant property of α-functionalization f α-oxo ketene dithioacetals, in recent years wehave realized halodecarboxylation, halodeacetylation, C–C coupling with Baylis-Hillmanaducts, acetylation, C–C coupling coupling with alcohols, multi-component reactions, etc. Onthe other hand, great advances in the construction of a diverse array of polysubstituted carbo-and heterocyclic compounds, such as cyclohexanones, unsymmetrical biaryls, coumarins,pyridines, indolizines, indole N-oxides, were also realized.The C–C bond forming reaction is an important research topic in organic chemistry. Theexploration of new carbon-carbon forming reaction on α-C of α-oxo ketene dithioacetals hasbeen the chief goal of our research. This thesis will show some new exploratory work in thisfield, and mainly includes three aspects:1. We have developed a new CuBr2and BF3·Et2O cocatalyzed [3+2] cycloaddition ofα-EWG ketene dithioacetals with p-quinones, which provides a simple and general methodfor the synthesis of polyfunctionalized benzofurans. This protocol is associated with mildreaction conditions, readily available starting materials, cheap catalysts and good yields. Thiscatalytic cyclization strategy provides a facile access to a wide variety of benzofuranscontaining rich functionality. These functional groups can provide opportunities for furtherelaboration of these benzofurans to2-aminobenzofurans and benzofuro [2,3-d]pyrimidines.2. A new allylic substitution of quinone monoacetals and ketene dithioacetals has beendeveloped (SN2). Accordingly, a range of substituted benzofurans was synthesized in high toexcellent yields from quinone monoacetals and ketene dithioacetals via a formal [3+2]cycloaddition under tin tetrachloride (1%) catalyzed. The advantages of the reaction,including its simplicity, rapidity, low catalyst loading of inexpensive tin tetrachloride, and inparticular, the regiospecificity. The reason of high regioselectivity and efficiency of thereactions is the coordination of tin tetrachloride to the two participants can put reaction centercloser, and which is called a pseudo-intramolecular process.3. We have developed a new method for the synthesis of bioactive coumestans fromquinone monoacetals and vi-nylogous thioesters via a formal [3+2] cycloaddition under tin tetrachloride catalyzed. The advantages of the reaction including mild conditions, simplicityand regiospecificity.