Base-Mediated Reaction of Hydrazones and Nitroolefins with a Reversed Regioselectivity: A Novel Synthesis of 1,3,4-Trisubstituted Pyrazoles
作者:Xiaohu Deng、Neelakandha S. Mani
DOI:10.1021/ol800200j
日期:2008.3.1
A regioselective synthesis of 1,3,4-tri- or 1,3,4,5-tetrasubstituted pyrazoles by the reaction of hydrazones with nitroolefins is described. Mediated with strong bases such as t-BuOK, the reaction exhibits a reversed, exclusive 1,3,4-regioselectivity. Subsequent quenching with strong acids such as TFA is essential to achieve good yields. A plausible stepwise cycloaddition reaction mechanism is proposed
描述了通过与硝基烯烃的反应的1,3,4-三-或1,3,4,5-四取代的吡唑的区域选择性合成。在强碱(例如t-BuOK)的介导下,该反应表现出反向的排他的1,3,4-区域选择性。随后用强酸(例如TFA)淬灭对于获得良好的收率至关重要。提出了合理的逐步环加成反应机理。