Study On Single Electron Transfer Reactions Of Carbon-sulfur And Carbon-silicon Bonds

Since the theory of single electron transfer was proposed,many organic reactions can be explained more reasonably.As the two means of single electron transfer reaction,visible light and single electron oxidant induced synthetic techniques have attracted more attention in recent years.Visible light is a kind of abundant clean energy.The visible-light-induced reaction was the features of mild conditions and simple operation.Persulfate is a single electron oxidant with strong oxidizing ability,low price and low toxicity which can produce stronger oxidative sulfate radical(SO₄^·-).In this thesis,visible light induced oxidative cleavages of C-S and C-Si bonds were investigated;the cleavage of C-Si bond and the formation of C-S bond promoted by persulfate were also studied.Moreover,the single electron transfer mechanisms of these reactions were studied.Heterocyclic compounds exist widely in medicines and natural products.In addition,heterocyclic structures play a significant role in the physiological activitiy.The C-S bond cleavage of ?-phenylthiol aromatic alcohols and derivatives has been fulfilled under visible light induction;and the as-generated benzyl cation turned to heterocyclic compounds via nucleophilic cyclization.Furan,pyran,lactone and pyrrole compounds could be synthesized employing Ru?bpy?₃Cl₂ as photocatalyst,blue LED as light source and air as oxidant.The reaction has many merits such as mild conditions,high reaction rate and good yield?68-87%?.The proposed mechanism suggested that ?-phenylthiol aromatic alcohols underwent single electron oxidation by Ru²⁺* or Ru³⁺,and generated benzyl cation by releasing phenylthio radical.Intramolecular cyclizations initiated by hydroxyl,carboxyl or amido lead to various heterocyclic compounds.Benzyl ethers are usually used as hydroxyl protection or synthetic precursor.We explored the photochemical etherification of benzyltrimethylsilanes with alcohol compounds.By application of visible light induced strategy with the blue LEDs as the light source,Ru?bpy?₃[PF₆]₂ as the photocatalyst and Cu Cl as the additive,benzyltrimethylsilanes undergo C-Si bond cleavage and react with alcohols leading to formation of ethers.A possible mechanisim indicated that a dual catalyst systems(Ru?bpy?3²⁺-S₂O₈^2-and SO₄^·-and Cu⁺-SO₄^·-)were involved,which were related to the formation of benzyl radical and benzyl cations,respectively.Hock process or Baeyer-Villiger oxidation are usually adopted to in the metal-free synthesis of phenolic compounds.We explored sodium persulfate promoted oxidation of benzyltrimethylsilanes which caused C-Si and C-C bond cleavage and produced phenols under the condition of heating at 55 ? and acetonitrile as solvent.GCMS analysis indicated the transformation of benzyl to carbonyl.Isotope labeling trials confirmed that the phenolic oxygen is originated from O₂,while the carbonyl oxygen is originated from Na₂S₂O₈.A plausible reaction mechanism was proposed that benzyltrimethylsilanes undergo desilianes,coupling with sulfate radical(SO₄^·-),further oxidation and adsorption of oxygen,finally intramolecular rearrangement led to phenol,sulfur trioxide and aldehyde/ketone.In the process of discussing mechanism,we also found the reaction of sodium persulfate with aromatic aldehyde can perform Baeyer-Villiger oxidation and give phenols,This method can be applied in actual production for neutral conditions.Thiocyanates are important and versatile synthetic intermediates due to their easy access to heterocyclic compounds,thiocarbamates,thiols and so on.We explored the reaction of thiols with sodium cyanide employing sodium persulfate as oxidant.Direct thiocyanates was realized under the condition of heating at 55 ?,DBU as base and acetonitrile as solvent.The proposed mechanism indicated thiocyanatobenzene was formed through nucleophilic attack of the cyano ion on diphenyldisulfane.