Dyi <sub> 2 </ Sub> And Metal Dy Application In Organic Synthesis

The metal-containing reagents are widely used in organic synthesis, according to statistic, more than 50 % new methods of organic synthesis are realized with the aid of metal-containing reagents, organometallic chemistry has become one of the most important and efficient tools for realizing the atom economy of reactions and the reduction of reaction conditions. Large numbers of studying results indicate that organolanthanides have some characteristic reactive chemistries differing from the organometallic complexes of main group metal and transition metal, they can provide an optimal geometrical environment for some reactions and have a tremendous potential in the exploitation of new reactions and methods. However, among the numerous reactive chemistries of lanthanide, low valent lanthanides also represent an important family. The most typical reagent is SmI₂, since it has been applied in organic synthesis in 1980 by Kagan, its application in organic synthesis remains flourishing. Nevertheless, the recent discovery of TmI₂, DyI₂, NdI₂ which are on behalf of new divalent lanthanide further enriched the divalent lanthanide chemistry, simultaneously, created a new era for the application of divalent lanthanide in organic synthesis. Because of their more powerful reductive ability than SmI₂, they can promote some reactions which can not be promoted by SmI₂, however, the study of their reactivity is on initial step, there still remains lots of unknown fields to be explored.The main target that this thesis study is: trying to use the strong reductive ability of DyI₂ to develop some new organic synthetic methodology which can complement with SmI₂．Fortunately, in this process, despite discovering that DyI₂ can promote some reactions which can not be promoted by SmI₂, we also found that metal Dy had more powerful reductive ability than SmI₂ in a certain condition. All these contents construct the present thesis. The whole thesis is divided into five chapters, the details are as follows:Chapter 1: The application of divalent lanthanide compounds in organic synthesis has been summarized, including the typical reagent SmI₂ and the new divalent lanthanide compounds DyI₂, TmI₂, NdI₂．Chapter 2: Investigated the coupling reactions of organic chlorides and ketones or aldehydes, at low temperature, without any additive, the yields of corresponding alcohols can reach 82-88%. However, in the same conditions, this reaction can not be promoted by SmI₂ even using carcinogenic HMPA, this is due to its less powerful reductive ability than DyI₂．As for the direct reactions of ketones or aldehydes and DyI₂, the formation of products can be controlled by adjusting the quantity of DyI₂, when DyI₂ is used as 1 equiv. as substrates, the pinacol coupling products are obtained, when DyI₂ is used as 2 equiv. to substrates, the products are corresponding alcohols. In addition, we found DyI₂ could catalyze the cycotrimerization of alkynes, while in the earlier work, the reactions of lanthanide complexes and alkynes could only afford linear polymers or dimers. We also found DyI₂ could efficiently catalyze the reactions of nitrils and amines, triazines or disubstituted amidines could be obtained by adjusting the ratio of nitrils and amines. More significantly, we found independent DyI₂ could promote the transformation of molecular dinitrogen to kinds of N-containing organic compounds, such as azines, amides, imides and phthalazine. Further more, we found that the product from burning metal Dy and DyCl₃ can also reduce dinitrogen gas to give ammonia after hydrolysis. All these results not only further enriched the reactive chemistry of DyI₂, but also clarified it is feasible to develop the catalytic amount reactions of DyI₂．Chapter 3: Free radical reactions are important tools in organic synthesis. One of the main achievements of this chapter is that we discovered DyI₂ could react with chlorosilanes to generate silyl radicals, and we have successfully applied it in organic synthesis and polymer science. Compared to conventional method, the main virtues of this method are: 1．Mild conditions, convenient manipulation. 2．Economical, the chlorosilanes used are rather cheap. 3．Avoiding the interference of H-transfer, multi radical centers, and organic initiators to the consequent reactions. It is more important that we found the existence of lanthanide could promote the selectivity of silyl radical reactions which extended its scope of application. For example, the DyI₂/SiCl₄ system can efficiently catalyze the cyclotrimerization of alkynes with high regio-selectivity, but SmI₂ can not substitute DyI₂．The system can also catalyze the polymerization of MMA, compared to this reaction catalyzed by other conventional free radicals, such as AIBN, the polymer obtained using the present method has higher molecular weight, higher syndiotactic contents, and smaller molecular weight distribution, this may be due to the cooperative action of resulting Dy³⁺ ion. It is noteworthy that the reactions above can not be promoted by silyl radicals from traditional methods using hydrosilanes as precursors, due to the competing H-transfer from hydrosilanes to alkyl radicals. Additionally, we also found DyI₂ could initiate the dehalogenation reactions of organic halides by tristrimethylsilylsilane (TTMSS), the results showed that the chlorides, bromides, and iodides tend to display an increasing reactivity in the order RCl < RBr < RI.Chapter 4: Considering the difficulty of preparing DyI₂, We tried to use more available and stable metal Dy to substitute DyI₂ to initiate silyl radicals. The results showed the strategy was feasible. Found that the Dy/SiCl₄ system can also efficiently catalyze the cyclotrimerization of alkynes and polymerization of MMA, while the reactions can not be occurred by using SmI₂/SiCl₄, which indicated lanthanide metals had more powerful reductive ability than SmI₂ in a certain condition. To extend our methodology, the Dy/Me₃SiCl promoted hydrosilylation of alkynes by TTMSS was also studied, it can give anti-Markovnikov products in Z-configuration with high regio-and stereo-selectivity. In addition, we have discovered a new reaction, it is that Dy/SiCl₄ can promote imines to give imidazolidines and tetrasubstituted hydrazines. This rare reaction can not be promoted by using silyl radicals from conventional method or lanthanide metal only. Finally, we found metal Dy could also efficiently promote the dehalogenation reactions of organic halides by TTMSS. The results in this chapter revealed for the first time the application of catalytic amount of lanthanide metal in organic synthesis.Chapter 5: When studying lanthanide initiated silyl radical reactions, we accidentally found that small amount of air could also promote the hydrosilylation of alkynes or alkenes and dehalogenation of organic halides by TTMSS, giving moderate to excellent yields under mild reaction conditions. These reactions are highly selective, economic, and clean, only require simple operation and avoid using metal complex catalysts or organic initiators.