Hemetsberger–Knittel and Ketcham Synthesis of Heteropentalenes with Two (1:1), Three (1:2)/(2:1) and Four (2:2) Heteroatoms

Reactions Pub Date : 2023-05-08 DOI:10.3390/reactions4020015
Z. Tokárová, R. Gašparová, Natalia M. Kabanova, Marcela Gašparová, R. Balogh
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引用次数: 0

Abstract

The synthetic methods leading to furo[3,2-b]pyrroles and thiazolo [5,4-d]thiazoles are reviewed herein. Furo-, thieno- and seleno [3,2-b]pyrroles are related to heteropentalenes, containing two heteroatoms in the entire structure, one each per core. The synthetic approach follows the Hemetsberger–Knittel protocol covering three reaction steps—the nucleophilic substitution of halogen-containing aliphatic carboxylic acid esters, Knoevenagel condensation and, finally, thermolysis promoting the intramolecular cyclocondensation to O,N-heteropentalene. The Hemetsberger–Knittel reaction sequence is also known for the preparation of O,N-heteropentalenes with three heteroatoms (2:1) and their sulphur and selen heteroatoms containing structural analogues and bispyrroles. The synthetic approach towards thiazolo [5,4-d] thiazoles represents a more straightforward route, according to the Ketcham cyclocondensation. Proceeding with the Ketcham process is more challenging since it occurs stepwise and the formation of by-products is obvious. Thiazolo [5,4-d]thiazole is a representative of the aromatic heteropentalene with four heteroatoms in the structure—twinned N and S, two for each of the five-membered rings. The synthetic approaches towards those particular heteropentalnes have been chosen as a consequence of our ongoing research dealing with the design, synthesis and applications of substituted furo [3,2-b]pyrroles and thiazolo [5,4-d]thiazole-based derivatives. While the furopyrroles are known for their pharmacological activity, thiazolothiazoles have become of interest to materials science. We are aware that from a “bank” of existing compounds/procedures not all are presented in this review, and we apologise to respective groups whose research have not been objectively included.
二(1:1)、三(1:2)/(2:1)和四(2:2)杂原子杂戊烯的Hemetsberger-Knittel和Ketcham合成
综述了呋喃[3,2-b]吡咯和噻唑[5,4-d]噻唑的合成方法。Furo-, thieno-和seleno [3,2-b]吡咯与杂戊烯有关,在整个结构中含有两个杂原子,每个核心一个。合成方法遵循Hemetsberger-Knittel协议,包括三个反应步骤-含卤脂肪羧酸酯的亲核取代,Knoevenagel缩合,最后是促进分子内环缩合成O, n-异戊二烯的热裂解。Hemetsberger-Knittel反应序列也以制备具有三个杂原子(2:1)的O, n -杂戊烯及其含有结构类似物和双吡咯的硫和硒杂原子而闻名。根据Ketcham环缩合,合成噻唑[5,4-d]噻唑的方法代表了更直接的途径。继续进行凯查姆工艺更具挑战性,因为它是逐步发生的,副产品的形成是显而易见的。噻唑[5,4-d]噻唑是芳香杂戊二烯的代表,在结构上有4个杂原子,N和S是孪生的,五元环各有两个。这些特殊杂戊烯酮的合成方法是我们正在进行的设计、合成和应用取代呋喃[3,2-b]吡咯和噻唑[5,4-d]噻唑衍生物的研究的结果。虽然呋喃吡咯以其药理活性而闻名,但噻唑噻唑已成为材料科学的兴趣所在。我们知道,并非所有的现有化合物/方法都在这篇综述中出现,我们向那些没有客观纳入研究的小组道歉。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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CiteScore
2.70
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