Calix[3]pyrrole: A Missing Link in Porphyrin-Related Chemistry
Calix[3]pyrrole: A Missing Link in Porphyrin-Related Chemistry
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DOI：
10.1021/jacs.1c06331
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发表时间：
2021-07-28
影响因子：
15
通讯作者：
Inokuma, Yasuhide
中科院分区：
文献类型：
--
作者：
Inaba, Yuya;Nomata, Yu;Inokuma, Yasuhide
卟啉化学中一个长期存在的问题是，为什么吡咯单体选择性地形成四吡咯大环，而相应的三吡咯大环却从未被观察到。杯[3]吡咯，一种带有三个sp(3)-碳连接的类似于三吡咯类大环的大环，是一个缺失的环节分子，可能是解开这个谜团的关键；然而，它仍然难以捉摸。本文报道了杯[3]吡咯及其呋喃类似物杯[3]呋喃的合成和应变诱导转化。这些大环很容易从环寡酮中获得。结晶学和理论分析表明，在已知的杯[n]型大环中，这三个亚单位体系具有最大的应变能。在卟啉环化条件下，环应变引发杯[3]吡咯首先转化为杯[6]吡咯，然后转化为杯[4]吡咯。目前的结果有助于解释为什么没有自然产生的三个吡咯大环，以及在经典的卟啉合成过程中没有观察到它们作为产物或中间体的事实。
A long-standing question in porphyrin chemistry is why pyrrole monomers selectively form tetrapyrrolic macrocycles, whereas the corresponding tripyrrolic macrocycles are never observed. Calix[3]pyrrole, a tripyrrolic porphyrinogen-like macrocycle bearing three sp(3)-carbon linkages, is a missing link molecule that might hold the key to this enigma; however, it has remained elusive. Here we report the synthesis and strain-induced transformations of calix[3]pyrrole and its furan analogue, calix[3]furan. These macrocycles are readily accessed from cyclic oligoketones. Crystallographic and theoretical analyses reveal that these three-subunit systems possess the largest strain energy among known calix[n]-type macrocycles. The ring-strain triggers transformation of calix[3]pyrrole into first calix[6]pyrrole and then calix[4]pyrrole under porphyrin cyclization conditions. The present results help explain the absence of naturally occurring three-pyrrole macrocycles and the fact that they are not observed as products or intermediate during classic porphyrin syntheses.