Uncommon aqueous media for nitrilimine cycloadditions. I. Synthetic and mechanistic aspects in the formation of 1-aryl-5-substituted-4,5-dihydropyrazoles
作者:Giorgio Molteni、Alessandro Ponti、Marco Orlandi
DOI:10.1039/b205063c
日期:2002.9.23
A number of 1-aryl-5-substituted-4,5-dihydropyrazoles 4 have been synthesised by 1,3-dipolar cycloaddition of variously substituted nitrilimines 2 onto the appropriate alkenyl dipolarophiles 3 in aqueous media and in the presence of a surfactant. Under these conditions, uncommon for the large majority of [3 + 2] cycloadditions, the electronic features of both the cycloaddends strongly dictate the reaction outcome. Clean and fast cycloadditions were observed between electron-rich nitrilimines and electron-poor dipolarophiles, while the reversal of the electronic features of the reactants gave poor results. Changes in surfactant concentration leads to some novel mechanistic insights.
已通过水性介质和表面活性剂存在下,各种取代的亚胺腈2与相应的烯基亲偶极体3的1,3-偶极环加成反应,合成了多个1-芳基-5-取代的4,5-二氢吡唑4。在这些条件下,对于大多数[3+2]环加成反应来说并不常见,环加成物的电子特征对反应结果影响显著。富电子的亚胺腈与贫电子的亲偶极体之间的环加成反应迅速且效率高,而反应物的电子特性反转则导致结果不佳。表面活性剂浓度的变化提供了一些新的机理见解。