Method for the Large-Scale Synthesis of Multifunctional 1,4-Dihydro-pyrrolo[3,2-b]pyrroles

Abstract

A thorough investigation has enabled the optimization of the synthesis of 1,4-dihydro-pyrrolo[3,2- b ]pyrroles. Although salts of such metals as vanadium, niobium, cerium, and manganese were found to facilitate the formation of 1,4-dihydro-pyrrolo[3,2- b ]pyrroles from amines, aldehydes, and diacetyl, we confirmed that iron salts are the most efficient catalysts. The conditions identified (first step: toluene/AcOH = 1:1, 1 h, 50 °C; second step: toluene/AcOH = 1:1, Fe(ClO 4 ) 3 ·H 2 O, 16 h, 50 °C) resulted in the formation of tetraarylpyrrolo[3,2- b ]pyrroles in a 6–69% yield. For the first time, very electron-rich substituents (4-Me 2 NC 6 H 4 , 3-(OH)C 6 H 4 , pyrrol-2-yl) originating from aldehydes and sterically hindered substituents (2-ClC 6 H 4 , 2-BrC 6 H 4 , 2-CNC 6 H 4 , 2-(CO 2 Me)C 6 H 4 , 2-(TMS-C≡C)C 6 H 4 ) present on anilines can be appended to the pyrrolo[3,2- b ]pyrrole core. It is now also possible to prepare 1,4-dihydropyrrolo[3,2- b ]pyrroles bearing an ordered arrangement of N -substituents and C -substituents ranging from coumarin, quinoline, phthalimide to truxene. These advances in scope enable independent regulations of many desired photophysical properties, including the Stokes shift value and emission color ranging from violet-blue through deep blue, green, yellow to red. Simultaneously, the optimized conditions have finally allowed the synthesis of these extremely promising heterocycles in amounts of more than 10 g per run without a concomitant decrease in yield or product contamination. Empowered with better functional group compatibility, novel derivatization strategies were developed.

Revisiting the non-fluorescence of nitroaromatics: presumption versus reality

“…Among known heteropentalenes, the pyrrolo[3,2- b ]pyrrole 105,106 core (PP) constitutes the most electron-rich scaffold. We have recently demonstrated that a simple pyrrolo[3,2- b ]pyrrole-based chromophore 51 bearing two peripheral 4-nitrophenyl groups (Fig.…”

Quadrupolar Dyes Based on Highly Polarized Coumarins

“… 18 In order to install coumarin units into these locations on this heterocycle, formyl-coumarin derivatives were designed for the recently optimized multicomponent reaction between aromatic amines, butane-2,3-dione, and aromatic aldehydes for the pyrrolo[3,2- b ]pyrrole synthesis. 19 The formyl-coumarin derivatives were additionally designed to possess an auxiliary CO 2 Me group at position 3 in order to increase their accepting character. The isomeric 6- and 7-formyl coumarins 2a and 2b designed for this purpose are shown in Scheme 1 .…”

Going beyond the borders: pyrrolo[3,2-b]pyrroles with deep red emission

“…Changes in the UV-Vis-NIR absorption spectra during polarization within the first oxidation peak revealed a decrease in the intensity of the bands at 468, 492 nm (1a) and 495 and 522 nm (1c) 59 ( Fig. 9 ), while the shift of the absorption in the infrared direction of the output bands of 1c indicates a decrease in the energy of the π–π* transition due to a partial localization of the HOMO orbital also on the pyridine rings.…”