Asymmetric Synthesis of a Bacteriochlorophyll Model Compound Containing <i>trans</i>-Dialkyl Substituents in Ring D
作者:Khiem Chau Nguyen、Pengzhi Wang、Roger D. Sommer、Jonathan S. Lindsey
DOI:10.1021/acs.joc.0c00608
日期:2020.5.15
preparation of a hybrid macrocycle (BC-1), which contains a trans-dialkyl group in ring D and a gem-dimethyl group in ring B. Stereochemical definition began with the synthesis of (2S,3S)-2-ethyl-3-methylpent-4-ynoic acid, a precursor to the trans-dialkyl-substituted AD dihydrodipyrrin. Knoevenagel condensation of the latter and a gem-dimethyl, β-ketoester-substituted BC dihydrodipyrrin afforded the enone (E
厌氧细菌光合作用的主要色素细菌叶绿素a(BChl a)从头合成的挑战包括在两个吡咯啉环(B和D)中同时形成大环和反式二烷基取代基。通过制备杂化大环(BC-1),其在D环中含有反式二烷基,已探索出在每个吡咯啉环中具有宝石二甲基基团的模型细菌叶绿素的已知途径,以用于合成BChla。立体化学定义始于合成(2S,3S)-2-乙基-3-甲基戊-4-炔酸,这是反式二烷基取代的AD二氢联吡啶的前体。后者与宝石-二甲基,β-酮酯取代的BC二氢联吡啶的Knoevenagel缩合得到烯酮(E,70%; Z,3%); N,1,2,3,5-三氯乙烷。随后的E-烯酮双环环化(通过Nazarov,亲电子芳族取代和消除反应)得到BC-1(53%的产率)以及微量的二氢卟酚副产物(荧光测定法相对于BC-1为1.4%) 。BC-1在D环中表现出所需的反式-二烷基立体化学,由于132-羰基甲氧基取代基的构型,以(预期)差向异构