Formation of Macrocyclic Ethers by Free Radical Cyclization: Effects of Chain Length, Substituents, and Solvents
作者:Annie Philippon、Marie Degueil-Castaing、Athelstan L. J. Beckwith、Bernard Maillard
DOI:10.1021/jo980259o
日期:1998.10.1
Free radical reduction by tributylstannane of omega-iodopolyoxaalkyl acrylates derived from tri-, tetra-, penta-, hexa-, and heptaethylene glycols gives mixtures of uncyclized reduction products and macrocyclic ethers formed by endo cyclization. The rate constants for cyclization of the intermediate radicals at 80 degrees C in benzene were determined under carefully defined conditions to be 15 x 10(4)
通过三丁基锡烷自由基还原衍生自三,四,五,五,六和七乙二醇的ω-碘多聚氧杂烷基丙烯酸酯,得到未环化还原产物和通过内环化形成的大环醚的混合物。在精心定义的条件下,确定80℃下苯中的中间体自由基环化的速率常数为15 x 10(4),13 x 10(4),5.1 x 10(4),10 x 10(4)和3.6 x 10(4)s(-)(1),分别用于形成12、15、18、21和24元环。这些值表明,与先前报道的烯基物质的环化相比,链中氧原子的存在使速率增加了10-30倍。苯在80摄氏度时的速率常数和甲基丙烯酸酯,巴豆酸酯,已经确定了8-碘-3,6-二氧杂辛醇的肉桂酸酯,马来酸酯和富马酸酯。在极性不同的溶剂中丙烯酸8-碘-3,6-二氧杂辛酯的还原表明环化速率具有相对较低的溶剂依赖性。