Selective Chlorination Of Vicinal Diols And Aerobic Oxidation Of Furan Derivatives

Chlorination of alcohol is one of the most important chemical reactions in organic synthesis.The selective chlorination of polyols is challenging due to chemical selectivity and regional selectivity,especially vicinal diols.In the first part of this paper,we studied the selective chlorination of vicinal diols.Formation of cyclic intermediates in situ during the chlorination may provide a solution to the monochlorination of vicinal diols.The strategy might avoid side reactions such as ether formation and rearrangement between molecules or within molecules and improve the selectivity of chlorination process.We used(Chloromethylene)dimethyliminium chloride Vilsmeier reagent or(Dichloromethylene)dimethylammonium chloride(Vehie's salt)as chlorination reagent to achieve the selective chlorination of vicinal diols under mild condition.The reaction was obtained chlorohydrin and chlorohydrin carbamate in moderate to good yields for a wide range of substrates.The chlorination protocol showed a wide functional tolerance of halogens,naphthalene rings,nitro,cyano and ester groups.It provided the effective method to synthesis chlorohydrin compounds.We speculated that chlorination protocol might not experience cyclic intermediates with Vilsmeier reagent.The good regioselectivity may arise from the discrimenation between benzyl alcohols and aliphatic primary alcohols under the optimized condition.However,the chlorination of diols with Vehie's salts underwent the cyclic intermediate and the substitution occurred by SN2 pathway.In the second part of this paper,the stereoselective aerobic oxidative ring opening of 2,5-disubstituted furans into 2-ene-1,4-diones.It often uses equivalent antioxidant to achieve oxidation of furans such as organic oxidizer or metal.It usually has equivalent waste form and low atom economy.Besides,this kind of oxidation is too expensive to large-scale reaction.It is attractive to develop aerobic oxidation of furan compounds.Nitroxyl radical are efficient oxidants which oxidation activity and selectivity of nitrous oxide can be improved by changing its structure.It can be used as a catalyst for recycling in the oxidation reaction,and can also combined with metal or non-metal catalysts to achieve aerobic oxidation.We will study the oxidation of furans compounds co-catalyzed by nitroxyl radical and non-metal catalysts.A method for synthesis of 2-ene-1,4-diketone was developed by adjusting the structure of nitroxyl radical,the types of non-metallic cocatalysts and optimizing the reaction conditions.