Bischler‐Napieralski Cyclization: A Versatile Reaction towards Functional Aza‐PAHs and Their Conjugated Polymers^†

Abstract

Nitrogen atom doped polycyclic aromatic hydrocarbons, the so‐called aza‐PAHs, and their conjugated polymers are applicable as functional chromophores and organic semiconductors. Prosperous developments of PAHs and heterocyclic chemistry have been made possible by considerable improvements in synthetic methodologies, among which one‐step reactions leading directly to an aza‐conjugated ring are highly desirable. Bischler‐ Napieralski cyclization, an old yet efficient reaction, can accomplish this task. During the last ten years, this reaction has been successfully used to synthesize a great variety of aza‐PAHs molecules. Further combination with polymer chemistry is able to provide the corresponding polymers. This feature article summarizes the up‐to‐data advances, mainly achieved by our groups, on the design and synthesis of new and well‐tailored aza‐PAHs and macromolecular architectures using Bischler‐Napieralski cyclization as the key step. Furthermore, the versatile applications of these functional materials in the fields of chemosensors, optoelectronic devices, and biomolecular probes are also covered in detail.

Angularly fused diaza-dinaphthopyrenes: regio-selective synthesis, crystal structures and isomer-dependent mechanochromic fluorescent properties

“…Our previous work has demonstrated that Bischler–Napieralski cyclization is a powerful approach to N-doping of PAHs, offering aza-PAHs such as phenanthridine, thiophene fused 1,10-phenanthroline, diazapyrene, 5,6,12,13-tetraazaperopyrenes, etc. 9 This reaction includes acylation and intramolecular electrophilic substitution. As for the pyrene ring, it is well known that electrophilic substitution occurs preferentially at its 1,3,6,8-positions.…”

Bischler–Napieralski Synthesis of Polycyclic N-Heteroaromatics Based on Tf2O-Promoted Electrophilic Activation of N-Aryl-2-Propynamides

“…Bischler–Napieralski (B–N) reaction was discovered in 1893 and has been widely used in organic synthesis, biology, and material science . Its nature is the electrophilic activation of an inactive 2° amide to form an active intermediate nitrilium salt by dehydration.…”

“…In a classic B–N reaction, POCl 3 is used as a popular activating agent at high temperatures. It has been limited to synthesize 3,4-dihydroisoquinolines and phenanthridines by intramolecular annulations because the chloride anion in nitrilium chloride is a good nucleophile. , In 2007, Movassaghi reported a modified B–N reaction using Tf 2 O/2-halopyridine (2-X-Pyr, X = F, Cl, I) as an activating agent to synthesize quinolines from N -aryl amides and alkynes 1 (Scheme ). This intermolecular B–N reaction was achieved efficiently because the counterion TfO – in nitrilium triflates has almost no nucleophilicity …”

Mechanistic Insights into Tf2O-Promoted Electrophilic Activation of 2-Propynamides and a New Synthesis of 2,4-Disubstituted Quinolines

“…Tf 2 O-promoted amide activation has important applications in the Bischler−Napieralski (B−N) reaction, which was discovered in 1893 and is well-known in the synthesis of Ncontaining heterocycles. 3 The nature of the B−N reaction is the electrophilic activation of a secondary amide by using POCl 3 as an activator. 4 An investigation showed that the efficiency of the B−N reaction has improved significantly when synthesis of 2,4-disubstituted quinolines 8 is developed (Scheme 2c).…”

“…Tf 2 O-promoted amide activation has important applications in the Bischler–Napieralski (B–N) reaction, which was discovered in 1893 and is well-known in the synthesis of N-containing heterocycles . The nature of the B–N reaction is the electrophilic activation of a secondary amide by using POCl 3 as an activator .…”