Benzylation Of Arenes And Heteroarenes Catalyzed By Hafnium And Copper Salts

Carbon-carbon bond forming reactions of arenes and heteroarenes are always the major topics in organic chemistry and organometallic chemistry. As one of these methods, Friedel-Cratfs reaction is important both in fundamental research and industrial application, so it is keeping to be a hotspot in the research from its birth to the present. But traditional Friedel-Crafts reaction has its own limitations, such as requirement of a stoichiometric amount of Lewis acid catalysts and large amounts of undesired products. Therefore, much attention is focused on the new Lewis acid catalysis system and expansion of different benzylating reagents.Benzylation of arenes and heteroarenes with benzyl alcohol catalyzed by HfCl4 is firstly studied in this dissertation, and the yields are 15-99%. In this catalysis system,14 kinds of different benzylating reagents are used in yields of 32-99%, among which 6 kinds of benzylating reagents are firstly applied to Friedel-Crafts alkylation. By detedcting reaction time and products, a serial of reactions are designed to propose and testify the reaction mechanism, which is in accordance with traditional benzyl positive ion process.On the basis of that, HfCl4/HfO2 system is developed to catalyze benzylation of benzyl alcohol in yields of 11-91% and other benzylating reagents in yields of 31-99%. The amount of HfCl4 has dropped to 10 mol%, meanwhile the HfO2 is recycled. The yields maintain 80% on after 5 cycles. This system also can catalyze the reaction of benzene with alkyl chloride, in which only the desired diphenylmethane is isolated in good yield (5 equiv.). And 10 equiv. diphenylmethane can be afforded with HfCl4/nano HfO2.Benzylation of arenes and thiophenes catalyzed by CuBr2/Fe system is firstly studied, mainly considering the effect of different metals with CuBr2 and the dehydration in process. The yields of the reaction with benzyl alcohol are 51-99%, and the yields of benzylation with other benzyl alcohols are 74-97%. A serial of reactions are designed to propose and testify the reaction mechanism, meanwhile, spectrum of reactant and intermediate product can be obtained by means of GC-MS. A possible reaction mechanism was that benzyl alcohol reacted with CuBr2 to give benzyl bromide. The benzyl bromide then reacted with arene in the presence of Fe to afford benzylation compounds. Under the premise of the mechanism, benzylation of benzyl bromide with Se and reaction of benzyl alcohol catalyzed by Fe/TCT (trichloro-1,3,5-triazine) have been studied.Furthermore, benzylation of methyl-substituted benzene by activation of saturated hydrogen through the use of oxidation or free radical initiation has been developed. By screening of organic catalysts, Lewis acid catalysts, metal catalysts and solvents for the model reaction, the best yield (123%, based on CuBr) of benzylation of toluene has resulted from the optimal condition under which the reaction is performed with BPO, Fe and CuBr in CCl4. Under this system, benzylation of benzene with different methyl-substitued arenes and heteroarenes have been investigated, in which the yield of the reaction with toluene is up to 83%. Lastly, benzylation of toluene, ethylbenzene and cumene catalyzed by Fe/CuBr2 in CCl4 has been developed, and the yields are 35-82%.In summary, a promising and short method for Friedel-Crafts-type chemistry have been developed by means of benzylation of arenes and heteroarenes with benzyl alcohol and other benzylating reagents catalyzed by HfCl4/HfO2 or CuBr2/Fe.