NH_(4)SCN-Promoted Formal[3+3]Annulation for the Synthesis of 5-Arylated Pyrazolo[1,5-a]pyrimidines

硫氰酸铵促进的[3+3]环化反应合成5-芳基吡唑并[1,5-a]嘧啶

A formal[3+3]annulation of 3-aminopyrazoles with cinnamaldehydes or cinnamyl alcohols mediated by NH_(4)SCN has been developed.This protocol provides a practical route to construct 5-arylated pyrazolo[1,5-a]pyrimidines with high functional group tolerance.The use of NH_(4)SCN as the cyanide anion surrogate allows the transient generation of cyanohydrin,which shifts the reactive center within cinnamaldehydes from formyl group to alkene group to realize an opposite regiocontrol comparing with previous reports.

报道了硫氰酸铵促进的3-氨基吡唑与肉桂醛或肉桂醇的[3+3]环加成反应,该方法为5-芳基化吡唑并[1,5-a]嘧啶化合物的合成提供了一种实用的合成途径,反应具有良好的官能团兼容性.值得注意的是,在I_(2)O_(5)存在下,硫氰酸铵作为氰基源,与肉桂醛反应生成瞬态的氰醇分子,能够将后续的反应中心从肉桂醛的醛基转移到烯基,从而实现与现有报道相反的区域选择性.