1,4-Dihydropyrrolo[3,2-b]pyrrole and Its π-Expanded Analogues

• Published in: Chemistry, an Asian journal Vol. 9; no. 11; pp. 3036 - 3045
• Main Authors: Janiga, Anita, Gryko, Daniel T.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.11.2014; WILEY‐VCH Verlag
• Subjects: aromaticity; electrophilic substitution; fluorescence; heterocycles; synthetic methods; fluorescence; heterocycles; electrophilic substitution; synthetic methods; aromaticity
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201402367

Various approaches to the synthesis of 1,4‐dihydropyrrolo[3,2‐b]pyrroles are summarized. Many two‐ and three‐step reaction sequences have been developed, and have allowed access to a broad variety of structures, including not only the parent 1,4‐dihydropyrrolo[3,2‐b]pyrroles, but also their π‐expanded analogues. The newest approaches are critically compared with older strategies. The reactivity of these compounds is also reviewed, with special emphasis on electrophilic aromatic substitution. The synthesis of indolo[3,2‐b]indole derivatives has been the subject of intense investigation. Overall, a few interesting and ingenious approaches toward these ladder‐type heteroacenes have been proposed, reaching total yields in the region of 30 %. Finally, the optical, electrochemical, and other physicochemical properties are presented in the broader perspective of heteropentalenes. The parent 1,4‐dihydro‐pyrrolo[3,2‐b]pyrroles constitute the most electron‐rich, simple, aromatic heterocycles, and their simple derivatives and π‐expanded analogues possess strong violet, blue, or green fluorescence both in solution and in the solid state. 1,4‐Dihydropirolo[3,2‐b]pirole i ich π‐rozszerzone pochodne przez długi czas pozostawały w cieniu swoich analogów zawierających siarkę. Jednak ich zalety w powiązaniu z nowymi metodami syntezy powodują renesans zainteresowania nimi. Metody otrzymywania tych związków są wyczerpująco przedstawione i krytycznie porównane. Omówiona jest również ich reaktywność oraz właściwości fizykochemiczne, ze szczególnym uwzględnieniem właściwości optycznych. Rediscovering old friends: Although indolo[3,2‐b]indoles (see picture) have been known for 130 years, their parent 1,4‐dihydropyrrolo[3,2‐b]pyrroles emerged in the 1970s and have only recently become easily accessible. Their synthesis, reactivity, and properties are exhaustively presented. OK