二氟甲基溴代腙与β-(N,N-二甲氨基)烯酮/丙烯酸酯/丙烯酰胺的[3+2]环化反应研究

[3+2]Cyclization of Difluoroacetohydrazonoyl Bromides withβ-(N,N-Dimethylamino)enones/Enoates/Enamides

报道了在碱存在下,由二氟甲基溴代腙原位生成的二氟甲基腈亚胺与β-(N,N-二甲氨基)烯酮/丙烯酸酯/丙烯酰胺的[3+2]环化反应.该反应首先产生了一个吡唑啉中间体,然后从该中间体上自发消除一分子二甲胺,最后以中等至良好的产率得到了一系列3,4-二取代-3-二氟甲基吡唑类化合物.该反应具有高度的区域选择性:即它是由1,3-偶极体的最低空轨道和富电子烯烃的最高占有轨道相互作用的反电子需求的环加成反应.该方法拓展了二氟甲基腈亚胺参与的[3+2]环化反应的类型,提供了一种简单、高效地合成3,4-二取代-3-二氟甲基吡唑类化合物的新方法.

A[3+2]cyclization of difluoromethyl nitrile imines generated in situ from difluoroacetohydrazonoyl bromides withβ-(N,N-dimethylamino)enones/enoates/enamides in the presence of base is described.The cycloaddition reaction pro-duced the pyrazoline intermediates,from which 3,4-disubstituted-3-difluoromethylpyrazoles were obtained in moderate to good yields via spontaneous elimination of the Me2NH molecule.The reaction is fully regioseclective by the interaction of lowest unoccupied molecular orbital(LUMO)of the 1,3-dipoles and highest occupied molecular orbital(HOMO)of electron-rich alkenes(inverse-electron-demand).This approach expands the types of[3+2]cyclization involved difluoro-methyl nitrile imines,which provides a simple,efficient and novel method for the synthesis of 3-difluoromethylpyrazoles.