Titanium-Mediated Cyclization of ω-Vinyl Imides in Alkaloid Synthesis: Isoretronecanol, Trachelanthamidine, 5-Epitashiromine, and Tashiromine
作者:Se-Ho Kim、Seok-In Kim、Sheng Lai、Jin Kun Cha
DOI:10.1021/jo9907383
日期:1999.9.1
A new method for the stereocontrolled synthesis of pyrrolizidine and indolizidine alkaloids by means of titanium-mediated cyclization of omega-vinyl imides is described. The general procedure involves treatment of readily available omega-vinyl imides 9 and 10 with 2.5 equiv of cyclopentylmagnesium chloride in the presence of ClTi(O-i-Pr)(3) (1.1 equiv) and subsequent stereoselective reduction of the
描述了一种新的方法,该方法通过钛介导的ω-乙烯基酰亚胺的环化立体控制合成吡咯烷和吲哚并立生物碱。一般程序包括在ClTi(Oi-Pr)(3)(1.1当量)存在下用2.5当量的环戊基氯化镁处理容易获得的欧米茄乙烯基酰亚胺9和10,随后立体选择性还原N-酰基组。顺式和反式环结立体异构体可以分别通过催化氢化(H(2),PtO(2),EtOAc)和NaCNBH(3)还原(TFA,MeOH)进行立体选择性制备。最后,用LAH或乙硼烷处理所得内酰胺以良好的收率得到目标生物碱1-8。