Synthesis of Tricyclic β-Methylene Spiro Lactones Related to Bakkenolides by Successive Radical Cyclization−High Pressure Diels−Alder Reactions
作者:Thomas G. Back、Patricia L. Gladstone、Masood Parvez
DOI:10.1021/jo960111+
日期:1996.1.1
piperylene failed at ambient pressure, but proceeded in generally good yield in the presence of various Lewis acids at pressures of ca. 16 kbar, to give mixtures of beta-exo, alpha-endo, and beta-endo cycloadducts 19, 21, and 23, respectively. The preponderance of endo products 21 and 23, formed via highly hindered, but more compact, transition states was attributed to the high pressure and resulted in trans-dimethyl
一些新的巴克内酯及其表位螺类似物的合成是通过一种新方法实现的。1-(苯基硒代)-2-氧代环戊烷羧酸烯丙基酯7-9的光解通过苯基硒代基团的基团环化作用产生相应的螺内酯10-12。亚硒酸酯11和12的亚砜消除产生相应的β-亚甲基内酯14和15。在环境压力下,内酯11与戊间二烯的狄尔斯-阿尔德环加成反应失败,但是在各种路易斯酸的存在下,在约200℃的压力下,通常以良好的产率进行。16 kbar,分别得到β-exo,α-endo和β-endo环加合物的混合物,分别为19、21和23。内在产物21和23的优势是通过高度受阻,但更为紧凑而形成的,过渡态归因于高压,并导致产物的反式二甲基构型。面部选择性取决于路易斯酸,使用TiCl(2)(OR)(2)类型的催化剂观察到最大的α:β比。通过外环氧化,区域选择性还原,氧化成相应的3-酮衍生物以及碱催化的平衡作用,可实现21和23中C-4甲基的差向异构体提供相应的顺式-二甲基类似物。