Selective C* halogenation (I and Br) of pyrazoles 1a, 3a and 4a gave halopyrazoles 5, 7–9, 11, 12. Reactivity differences between 1a, 3a and 4a, and the failure of 2a to give the expected halopyrazoles 6, 10 were explained using calculated relative energies of bromination, and inspection of frontier molecular orbitals. Utility of the prepared halides was demonstrated by a series of palladium-catalysed cross-coupling reactions.
对
吡唑 1a、3a 和 4a 进行选择性 C* 卤化(I 和 Br),可得到卤
吡唑 5、7-9、11、12。1a、3a 和 4a 之间的反应差异,以及 2a 未能得到预期的卤代
吡唑 6、10 的原因,可以通过计算
溴化相对能量和检查前沿分子轨道来解释。一系列
钯催化的交叉偶联反应证明了所制备卤化物的实用性。