Dibenzopyrrolo[1,2-a][1,8]naphthyridines: Synthesis and Structural Modification of Fluorescent L-Shaped Heteroarenes

Abstract

The L-shaped, π-extended pentacycle dibenzopyrrolo[1,2-a][1,8]naphthyridine and its derivatives were synthesized using two methods: fully intramolecular [2 + 2 + 2] cycloaddition and oxidative aromatization using substituted carbodiimide and modification of an electron-rich indole ring of an L-shaped skeleton via electrophilic reaction and cross-coupling. These L-shaped compounds emitted fluorescence in high quantum yield. The position of substituents affected the fluorescence color through two different mechanisms, π-conjugation and skeletal distortion, which caused the substituted L-shaped compounds to emit fluorescence in a variety of colors and to exhibit solvato-fluorochromism.

Accessing [g]-Face π-Expanded Fluorescent Coumarins by Scholl Cyclization

“…Particularly, the large molar extinction coefficient of 12g / 12h is more likely due to its large π-system. The emission spectrum of 12a–e , g was featureless resembling other heteroarenes, and their emission maximum was found to be in the range 410–590 nm, which covers the blue to cyan to yellow emission region (Figure b and Supporting Information). The featured emission profile in 12f and 12h , despite having ICT, may presumably be attributed to the coupling of locally excited (LE) states with the charge transfer (CT) states .…”

Aromatic Aza‐Claisen Rearrangement of Arylpropargylammonium Salts Generated in situ from Arynes and Tertiary Propargylamines

“…The above reaction, we discovered, represents a new type of aromatic aza‐Claisen rearrangement of ammonium salts, and moreover, it might evolve into a unique yet powerful approach for the synthesis of 2‐propargylanilines in a regiospecific manner [4, 5] . Therefore, we decided to optimize the reaction conditions to improve the yield for the formation of 2‐proparylaniline 3 b [15] .…”

“…Principally, the aromatic aza‐Claisen rearrangement of arylpropargylammonium salts would produce 2‐allenylanilines, [3] which might further isomerize to 2‐propargylanilines under certain conditions. To date, there are only sporadic examples available for the synthesis of 2‐propargylanilines including Friedel–Crafts propargylation of 4‐substituted anilines [4] and multistep transformation of 2‐azidobenzophenone [5] . Herein, we report that arylpropargylammonium salts, generated in situ from arynes and tertiary propargylamines, participate in the aromatic aza‐Claisen rearrangement followed by isomerization to afford 2‐propargylanilines, which further cyclize in the presence of aluminum chloride to yield multisubstituted indoles (Scheme 1 B).…”

Fluorescent Short‐Stranded Helical Foldamers Based on L‐shaped Dibenzopyrrolo[1,2‐a][1,8]naphthyridine

“…To examine the conformations of the dimers in solution, 1 H NMR spectra of the dimers 1 – 3 and the fixed‐helical dimer trans ‐ 4 were measured in CDCl 3 along with monomeric unit 16 as a reference compound (Figure and Figure ). We found that the extents of the upfield shifts for the terminal aromatic protons H B and H C of the L ‐shaped pentacycles and the downfield shifts for the aromatic protons H M , H L , and H a around the spacer unit reflected the proportion of the dimers in each helical form in solution.…”

“…recently reported the synthesis and optical properties of the L‐shaped pentacycle, dibenzopyrrolo[1,2‐ a ][1,8]naphthyridine . The L ‐shaped pentacycle contains several prominent features as a monomer unit for a highly fluorescent helical foldamer: L‐shaped curved planar skeleton, solvent‐independent high fluorescence quantum yield, and structural modification capability at various positions (Figure a).…”