Dipartimento di Ingegneria e Scienze Applicate, Università di Bergamo, 24044 Dalmine, Italy.
Dipartimento di Chimica, Materiali e Ingegneria Chimica Giulio Natta, Politecnico di Milano, 20131 Milan, Italy.
Molecules. 2022 Apr 14;27(8):2522. doi: 10.3390/molecules27082522.
Functionalization, namely the introduction of side groups onto the molecular scaffold of a helicene, may have either the purpose of modifying the electronic properties of the parent helicene, e.g., by adding electron-withdrawing or electron-donating groups, or the scope of providing the helicene with a "handle", which can be reacted to bind the molecule to another molecule or to a solid structure, such as a carbon or metal surface, or again to allow for complexation of the helicene with metal ions. The possible approaches are two-fold: the synthesis of the helicene can be performed using starting materials that already contain a side group, or the side group can be introduced after the synthesis of the parent helicene. As azahelicenes are helicenes bearing one or more nitrogen atom(s) in the molecular framework, parent azahelicenes can be functionalized on carbon atoms by exploiting the presence of the electron-withdrawing nitrogen atom. Moreover, they can be transformed into quaternary salts, whose properties are quite different from those of the parent azahelicenes in terms of the solubility and electronic properties. This review aims to provide a survey of the different synthetic methods available to attain this fascinating class of compounds.
功能化，即向螺旋烯分子支架中引入侧基，其目的可能是修饰母体螺旋烯的电子性质，例如通过添加吸电子或供电子基团，或者为螺旋烯提供“手柄”，可以通过反应将分子与另一个分子或固体结构（如碳或金属表面）结合，或者再次允许螺旋烯与金属离子络合。可能的方法有两种：一种是使用已经含有侧基的起始原料来合成螺旋烯，另一种是在合成母体螺旋烯之后引入侧基。由于氮杂螺旋烯是分子骨架中含有一个或多个氮原子的螺旋烯，因此可以利用吸电子氮原子的存在，在碳原子上对母体氮杂螺旋烯进行功能化。此外，它们可以转化为季铵盐，其性质在溶解度和电子性质方面与母体氮杂螺旋烯有很大的不同。本综述旨在提供获得这一迷人化合物类别的不同合成方法的概述。
