The Research On The Conversion Of C=O Bond To C?N Bond And The Cyclization Of Ketones

Ketones are one of the most versatile and fundamental class of compounds, the transformation of ketones has attracted the continuous attention of chemists. The conversion of the C=O bond of ketones to a C-O bond, a C-C bond, a C=C bond, a C-N bond or a C=N bond, the oxidation of the a-C-H bond of ketones and the cyclization of ketones have already been well developed, and many innovative research results have been achieved. Nevertheless, the conversion of the C=O bond of ketones to a C?N bond has not been described. Despite the significance of the cyclization of ketones, these developed protocols suffer from the limited substrate scopes and stoichiometric metal salts. Therefore, it is of great significance to develop a novel conversion of C=O bond of ketones to a C=N bond and an environmentally benign cyclization of ketones via the transformation of the C=O bond. In this paper, we studied the novel conversion of C=O bond of ketones to a C=N bond and the environmentally benign cyclization of ketones via the transformation of the C=O bond, respectively. The contents are as follows:(1) The conversion type of the C=O bond of ketones and other transformations of ketones were summarized. The significance, source and main content of this topic were also illustrated.(2) The conversion of the C=O bond of ketones to a C=N bond was studied systematically. Firstly, the reaction conditions were optimized. The optimum reaction conditions were confirmed:acetophenone (1.0 mmol), NH4(CO3)2 (1.0 equiv.), Cu(OAc)2 (30 mol%), Tetrabutyl ammonium iodide (30 mol%), Dimethyl sulfoxide (3.0 mL),120?,5 h, oxygen (1 atm). Then the generalities and limitations of this conversion were investigated. The results showed that both aromatic ketones and aliphatic ketones could realize the conversion of the C=O bond to a C?N bond under the standard conditions, and it also has high functional group compatibility. Subsequently, the applicability of other carbonyl compounds is also investigated, the results showed that only aldehydes could realize the C=O bond to a C?N bond.(3) The cyclization of ketones via the transformation of the C=O bond was studied systematically. Firstly, the factors which could effect on the reaction such as catalyst, reaction temperature, reaction time and solvent were investigated, and the optimal reaction conditions were determined:acetophenone (0.5 mmol), NH4OAc (3 equiv.), T(p-OMe)PPFeCl (1.0 mol%), Dimethyl sulfoxide (2.0 mL),120?,24 h, oxygen (1 atm). Then the generalities and limitations of this conversion were investigated. The results showed that all of the methyl ketones, alkyl ketones and 1,3-diketones could could achieve the cyclization reaction to gained ploy-substituted pyridines, and the transformation also has high functional group compatibility. However, the use of 1,2-diketones as a substrate under the standard conditions resulted in the 2,4,5-trisubstituted oxazoles as the products.(4) The mechanism of the conversion of the C=O bond of ketones to a C=N bond and the cyclization of ketones via the transformation of the C=O bond was investigated, respectively. According to the results of the control experiments and the reported literatures, the possible reaction mechanism was proposed for the transformation of ketones, respectively.