Study On Construction Of C-Heteroatom Bonds From Alcohols Catalyzed By Br(?)Nsted Acid

Carbon-heteroatom bond is widely found in drugs and natural molecules,and its construction is one of the important research fields today.However,in the process of carbon-heteroatom bond construction,transition metals are often used as the catalyst,leading to high cost,lots of by-products and environmental problems.Even in metal-free catalytic systems,an equal or excess amount of strong base or oxidant is required.Meanwhile,alcohols have the characteristics of economy,greenness and low toxicity,and can accept the attack of many nucleophiles to build carbon-heteroatom bond.Green solvents replacing traditional organic solvents can optimize the reaction process,and solve problems such as environmental pollution and harm to human health.Considering the development of Green Chemistry,it is urgent to develop more green,mild,simple,efficient,and highly selective catalytic systems to realize the conversion of alcohols.Br(?)nsted acids such as Bu₄NHSO₄ and H₃PW₁₂O₄₀·x H₂O,due to their easy separation and high catalytic efficiency and so on,can efficiently activate alcohols to form carbocation intermediates under mild conditions,which can accept the attack of nucleophiles.Therefore,Br(?)nsted acids are expected to play an active role in the construction of carbon-heteroatom bonds.Based on this,this dissertation focuses on the construction of carbon-heteroatom bonds from alcohols with various nucleophiles comtaining N,O and P catalyzed by Br(?)nsted acids in green solvent such as water or dimethyl carbonate.The research content mainly includes the following three aspects:1.The direct N-allylation reaction of pyrazole and its derivatives in the aqueous phase to construct C-N bonds was catalyzed by Bu₄NHSO₄,generating up to 93%yield.The metal-free system avoided the use of any additives.After the catalyst was reused for 6 times,the activity did not decrease substantially,and the system was also suitable for gram-scale reaction.It was found that allylic ether was not an intermediate in this reaction.Control experiments and density functional theory(DFT)calculations indicated the existence of hydrogen bonding between the reaction substrates,solvent and catalyst,especially the hydrogen bonding effect between allylic alcohol and water.A mechanism involving the action of Bu₄NHSO₄ and hydrogen bonding,carbocation attacked by nitrogen-containing nucleophiles to generate allylamines was proposed.2.Using the heteropolyacid H₃PW₁₂O₄₀·x H₂O as the catalyst and dimethyl carbonate as the solvent,the oxyalkylation of oxime and alcohol to construct a new C-O bond was realized.The system had wide substrate scope:the reaction of acetophenone oxime,benzophenone oxime and triphenylmethanol could be realized at room temperature,providing above 90%yields;aliphatic ketoximes can react with triphenylmethanol and benzophenone oxime can react with aliphatic tertiary alcohols smoothly;and the reaction of the substrates containing heteroatoms can also occur.The spectra characterization such as UV-Vis,NMR and FT-IR,and control experiments indicated that the reaction underwent a carbocation process,and there was a hydrogen bond between the anion of H₃PW₁₂O₄₀·x H₂O and the hydroxyl group of triphenylmethanol.3.A green catalytic system comprising phosphotungstic acid was developed for the phosphorylation reaction of secondary benzyl alcohol and secondary phosphine oxide to build C-P with dimethyl carbonate as the green solvent.The yield was up to 96%and the system was also suitable for allylic alcohol and triphenylmethanol.And the activities of phosphine oxides would not be affected by electronic effects and steric hindrance effects.At the same time,the possible mechanism that the reaction could pass through the diphenyl carbocation intermediate was proposed.