Facile and Multistep Synthesis of Functionalized Nitroxide Radicals Containing a Bipyridine Frame
作者:Raymond Ziessel、Abdelkrim El-ghayoury
DOI:10.1055/s-2000-8730
日期:——
The synthesis of stable bipyridine substituted nitronyl-nitroxide (NIT) or imino-nitroxide (IM) is reported. These methyl or ethynyl functionalized compounds have been prepared from the bromo-substituted analogues by a carboalkoxylation reaction catalyzed by low valent palladium(0) using carbon monoxide in the presence of a primary alcohol as nucleophile and a tertiary amine as base. In the case of the 6,6′-dibromo-2,2′-bipyridine, a quite selective mono-carboethoxylation reaction is achieved under mild conditions (70 °C, 1 atmosphere CO). Stepwise reduction of the resulting esters with sodium borohydride, followed by Swern oxidation, affords the corresponding carbaldehydes in good yield. Furthermore, these derivatives were used in a multistep protocol to prepare hybrid molecules bearing both an ethynyl group and a nitroxide free radical. The synthetic methods reported herein provide a practical methodology to the rational design of ligands bearing different kinds of functionalities.
本研究报道了稳定的双吡啶取代亚硝酰-亚硝基氧化物(NIT)或亚氨基-亚硝基氧化物(IM)的合成。这些甲基或乙炔基官能化化合物是在低价钯(0)的催化下,以伯醇为亲核体,叔胺为碱,通过一氧化碳的羧烷氧基化反应,从溴取代的类似物中制备出来的。就 6,6′-二溴-2,2′-联吡啶而言,在温和的条件下(70 °C,1 个大气压 CO),可以实现相当有选择性的单羧乙氧基化反应。用硼氢化钠逐步还原生成的酯,然后进行斯韦尔恩氧化反应,就能以良好的收率得到相应的羧醛。此外,这些衍生物还被用于制备同时带有乙炔基和亚硝基自由基的杂化分子的多步方案中。本文报告的合成方法为合理设计具有不同功能性的配体提供了实用的方法。