Study on the synthesis mechanism of pyrazoles via [3+2] cycloaddition reaction of diazocarbonyl compounds with enones without leaving groups

On the basis of the density functional theory (DFT), the process of cycloaddition reaction of diazocarbonyl compounds with enones without leaving groups to obtain pyrazoles was proposed. First, the diazocarbonyl compounds reacted with enones to offer the intermediates by cycloaddition reaction, which was captured of hydrogen of the intermediate by the base to offer the nonaromatic pyrazole intermediate, which then give the final product by oxidation and isomerization in the air. This protocol corrected the reaction mechanism that was proposed in the experimental section. The negative correlation between the yields of products with the charges of ADCH at the C1 position of enones was also founded, which was consistent with the experimental results. The protocol could provide theoretical guidance for designing more efficient cycloaddition reaction.