The Study On Dioxiranes For Its Oxidation

Dixorane is an excellent,harmless,and new-style oxidized reagent.Its peculiar oxidation function has been widely admitted by the majority of chemists since it was discovered.Above all it has been playing an important role in the organic synthesis,especially in the drug synthesis.To investigate its oxidation function deeply and broaden the scope of its application,the three main researches were performed in this paper.(1)Some alkenes,amines and alcohols were respectively oxidized by dioxiranes.At the same conditions,the various substrates which belong to the same variety were investigated.The experimental results indicate that dioxiranes are highly efficient,selective and mild epoxidation reagent;the procedure which dioxiranes oxidized alkenes,amines and alcohols is a kind of the concerted reaction;to alkenes,to some extent,the results of the oxidation were determined by the property of the substrates.Generally speaking,First the alkene with the electron-withdraw group in its double bond is much easier to be oxidized than the alkenes with electron-donate group in its double bond.Second the performance of oxidation is related to the steric hindrance of the alkenes.To amines,the primary amines is oxidized into the nitro product;the secondary amines is turned into the hydroxylamine;the tertiary amine is formed into the amine N-oxides. Furthermore,among the three type of the amines,the primary amines is easy to be oxidized,and the tertiary amine is the most difficult to be oxidized.To alcohols,the primary alcohol is oxidized into the aldehyde;the secondary alcohol is turned into ketone;the tertiary alcohol can not be oxidized.(2)Induced byβ-CD,Dioxiranes can succeed in performing the asymmetric epoxidation of the alkenes.Nowadays dioxiranes is usually generated with Oxone and ketone in situ.In this paper,In view of H₂O₂ is harmless and friendly to environment,a kind of new means for producing dioxiranes is designed with CH₃COCF₃,H₂O₂ and CH₃CN;some various structures of ketones and solvents were investigated.The asymmetric epoxidation of styrene was investigated by this kind of oxidant in the presence ofβ-CD.At the different conditions,the molar ratio of theβ-CD/styrene,the amount of NaHCO₃ and ketone were optimized.The experimental outcome shows that the oxidant has good influence on the oxidation of styrene;the asymmetric epoxidation of styrene can be induced by theβ-CD.(3)While the asymmetric epoxidation of styrene is induced by theβ-CD, the extra ketone is needed to add to generate dioxiranes.Because the hydroxyl groups of theβ-Cyclodextrin have various activity,a kind of new synthetic ideas was formed that the mono(2-O-hydroxypropyl) -β-cyclodextrin was synthesized selectively fromβ-Cyclodextrin,and then it was oxided and turned into aβ-Cyclodextrin-modified ketone by dioxiranes.Without adding the other ketone to the reaction,Dioxirane was produced with theβ-Cyclodextrin-modified ketone and Oxone.In the presence of Dioxirane,theβ-Cyclodextrin-modified ketone is used as a supermolecular catalyst for stereoselective epoxidation of styrene.The effect factors on asymmetric epoxidation of the styrene such as the molar ratio of theβ-Cyclodextrin-modified ketone/styrene,the amount of NaHCO₃ and Oxone,reaction time and temperature have been examined.The experimental results indicated that the 2-O-(prop-2-one-yl)-β-Cyclodextrin is a good catalyst to the epoxidation of styrene;when the reaction time is 5h,the molar ratio of theβ-Cyclodextrin-modified ketone,Oxone,NaHCO₃ and Styrene is 2:6:12:1,the maximum enantiometric excess of 1,2-epoxyethylbenzene was up to 13%.