New hydroxy-pyrazoline intermediates, subtle regio-selectivity and relative reaction rate variations observed during acid catalyzed and neutral pyrazole cyclization
作者:Timothy Norris、Roberto Colon-Cruz、David H. B. Ripin
DOI:10.1039/b500413f
日期:——
capability of the R and Ar substituents. The reaction conditions that caused cyclization to pyrazoles varied from direct condensation of the hydrazine and 1,3-dicarbonyl compounds, to reactions requiring catalytic quantities of sulfuric acid to sulfuric acid in excess. Unexpected regio-selectivity was observed in the case of R = CF3 that depended upon the reaction conditions.
芳肼4和1,3-二羰基化合物5通过via异构体对6和7失水而反应生成吡唑,这会产生两种可能的区域异构体。有时观察到3-羟基-3,4-二氢吡唑或羟基吡唑啉9和9是稳定的可分离中间体,可以在失去第二分子水生成吡唑10和11之前对其进行充分表征。类型8和9的中间体相对较少。我们研究了其中R = CH3,CHF2和CF3,Ar = Ph和5-甲磺酰基吡啶-2--2-基的反应系列(方案2),并观察了动力学行为和区域异构现象之间的性质差异,具体取决于电子的程度。 R和Ar取代基的吸收能力。导致环化成吡唑的反应条件从肼和1,3-二羰基化合物的直接缩合到需要催化量的硫酸到过量硫酸的反应之间变化。在R = CF 3的情况下,观察到区域选择性超出预期,这取决于反应条件。