Carboxylation Of Terminal Alkynes With Carbon Dioxide As Synthon And Selective Oxidation Of Sulfides

As the principal greenhouse gas, carbon dioxide is also a ubiquitous, nontoxic, safe, renewable C1resource. However, the chemical inertness associated with its thermodynamic and kinetic stability pose major challenges for selective carbon dioxide transformation. The utilization of carbon dioxide has been severely hampered by the limited scale and products of industrial transformation. The use of CO2as a chemical feedstock will almost certainly not reduce its atmospheric concentration significantly; however, it may provide sustainable access to high-value products from a nontoxic, renewable, and low-cost resource.Oxidation of organic sulfides is one of the most direct methods to synthsis sulfoxide or sulfone compounds, and also a widely used oxidative desulfurization technique. The oxidation needs a stoichiometric amount of oxidant, which has been severely hampered by high pressure operation or waste emissions. Development of environmentally friendly, easy oxidation method to realize selectivity control of sulfide oxidation reaction to sulfoxide and sulfone, respectively, is of great significance.This dissertation, which focuses on the research field of green chemistry and CO2chemistry, has two parts including the carboxylation of C(sp)-H bonds using CO2as carboxylative reagent and controlled selective oxidation of sulfides.1) The carboxylation of terminal alkynes with ambient CO2was achieved under mild conditions using ethylene carbonate as solvent without additional ligands. A range of terminal alkynes with electron-withdrawing group or electron-donating group, and various alkyl halides could undergo the coupling reaction smoothly. Moreover, the reaction of terminal alkyne with CO2could successfully run on gram scale. DFT calculations reveal that the energy barrier of CO2insertion step could be reduced by employing ethylene carbonate as solvent and ligand. Such findings in this study may be of great interest to stimulate development of novel accesses to carboxylic acid from hydrocarbons and CO2in green solvent.2) The carboxylation of terminal alkynes with CO2was investigated using ethylene carbonate as solvent and activated carbon supported CuBr as catalyst without other ligands or additives. Reasonable yields were obtained in the presence of CO2balloon after two hours of reaction. In addition, the heterogeneous catalyst is stable to air and moisture and can be easily recovered and reused.3) Tert-butylnitrite was proved to be an efficient oxidant for the selective oxidation of sulfides to sulfoxides. The reaction was promoted by Fe(NO3)3·9H2O under mild conditions and various substrates were effectively converted into the corresponding sulfoxides in good to excellent yields. The noteworthy feature could be that the procedure avoids the use of corrosive HBr by using an inexpensive Fe(Ⅲ) reagent as a promoter, tert-butylnitrite as a convenient liquid oxidant.4) Selective oxidation of sulfides was successfully performed by employing oxone (2KHSO5·HSO4·K2SO4) as oxidant without utilization of any catalyst or additive under mild conditions. Notably, the reaction can be controlled by the chosen solvent. When ethanol was used as the solvent, sulfoxides were obtained in excellent yield; the reaction almost exclusively gave the sulfone in water. Furthermore, this protocol worked well for various sulfides to the corresponding sulfoxides in ethanol or sulfones in water. Additionally, the sulfone product could be easily separated from the reaction mixture.5) Selective oxidation of sulfides was successfully performed by employing phenyliodine diacetate as oxidant with the catalysis of TsOH in aqueous solution under mild conditions. Sulfoxides were formed with1.1equiv. of PhI(OAc)2at room temperature; whereas sulfones were obtained in the presence of2.1equiv. of PhI(OAc)2at80℃under otherwise identical conditions. Notably, various sulfides were converted to corresponding sulfoxides or sulfones in good to high yields by this metal-free protocol. The reactive oxidant was proposed to be Koser’s reagent generated in situ from readily available phenyliodine diacetate and only10mol%of TsOH, which avoided the prior synthesis of Koser’s reagent with stoichiometric additives.