Efficient Synthesis of Dipyrrolobenzenes and Dipyrrolopyrazines via Bidirectional Gold Catalysis: a Combined Synthetic and Photophysical Study

Abstract

New N-heterocyclic fluorophores are sought-after compounds for organic electronic devices. Here, we report on a straightforward synthesis to access meta/para-dipyrrolobenzenes and para-dipyrrolopyrazines in high yields using a bidirectional gold-catalyzed cyclization strategy. The versatility of our reaction protocol was showcased by preparing dipyrroloarenes with different substituents, various functional groups, and in a multitude of substitution patterns. Furthermore, we showed that the dipyrroloarenes can be post-modified by N-alkylation to improve the solubility or bromination to yield precursors for further derivatization via cross-coupling. Investigation of the photophysical properties of themostly unprecedenteddipyrroloarenes identified strong blue emitters such as the diphenyl metadipyrrolobenzene with a quantum yield of 98%. Moreover, we showed that changes in the solvent polarity or interactions with Lewis acids such as borane can be used to fine-tune the photophysical properties of the fluorophores.

Gold‐Catalyzed Bidirectional Access to Planar Heptacyclic Benzobispyrido[1,2‐a]indoles and Benzobispyrrolo[1,2‐a]Quinolines for Materials Science

“…The syntheses of the substrates for the BBPQ compounds turned out to be more challenging (Scheme 2b). Lacking any literature for synthesizing 2,6‐alkyne‐substituted benzodipyrroles or similar compounds, we developed an approach starting from 2,5‐diiodo‐ N 1 , N 4 ‐diphenylbenzene‐1,4‐diamine ( 4 ), which is accessible via reductive amination of 2,5‐diiodocyclohexa‐2,5‐diene‐1,4‐dione ( 3 ) [12] . A Sonogashira cross‐coupling with protected phenylbutadiyne 5 yielded bidirectional diyne 6 , which partly cyclized during the reaction.…”

“…Lacking any literature for synthesizing 2,6alkyne-substituted benzodipyrroles or similar compounds, we developed an approach starting from 2,5diiodo-N 1 ,N 4 -diphenylbenzene-1,4-diamine (4), which is accessible via reductive amination of 2,5-diiodocyclohexa-2,5-diene-1,4-dione (3). [12] A Sonogashira cross-coupling with protected phenylbutadiyne 5 yielded bidirectional diyne 6, which partly cyclized during the reaction. Treatment by gold catalysis led to cyclized benzodipyrrole 7 a in an overall yield of 65% over two steps.…”

“…), aniline (15 eq. ), chlorobenzene, 90-135 °C, 16 h. [12] v) 2-Methylbut-3-yn-2-ol (1 eq. ), (bromoethynyl)benzene (1.1 eq.…”

Versatile access to nitrogen-rich π-extended indolocarbazolesviaa Pictet–Spengler approach

“…Fortunately, we lately developed a versatile gold-catalyzed [51][52][53][54][55][56][57][58][59] method for the building of benzodipyrroles and therein showed the example of bis(2-aminophenyl)-substituted benzodipyrrole 1 (Scheme 2). 60 This substrate is accessible starting from 1,4-diiodo-2,5-dimethoxybenzene in a straightforward four step synthesis and should be suitable for the synthesis of BBPQs via the PSR. As a first attempt in synthesizing an example of a BBPQ, we started with similar reaction conditions as used within the preceding, monodirectional work.…”

Au → M bonds promote catalytic alkyne hydrofunctionalisation

“…1 This property has been used successfully to develop powerful π-acid catalysts for organic synthesis. 2 The Dewar–Chatt–Duncanson model for π-ligand coordination suggests that the π-acidity of Au I -complexes increases when electron-deficient spectator ligands are used which promote the backbonding to the π-ligand. Alcarazo et al exploited this concept for Au I and Pt II -complexes using α-cationic phosphine ligands.…”