Tandem Synthesis of Benzo[b]carbazoles and Their Photoluminescent Properties

Abstract

5 H-Benzo[b]carbazoles were prepared through a tandem reaction between 2-ethynyl-N-triphenylphosphoranylidene anilines and α-diazoketones through ketenimine intermediates in moderate-to-good yields. By using this approach, benzo[b]benzo[5,6]indolo[3,2-h]carbazoles, fluoreno[9,1-ab]carbazoles, and fluoreno[9,1-ab]fluoreno[1',9':5,6,7]indolo[3,2-h]carbazoles were constructed in one pot. Moreover, the resulting products emitted light within the range 410-521 nm, with quantum yields of up to 62 %.

Recent Developments in the Cyclization of Alkynes and Nitrogen Compounds for the Synthesis of Indole Derivatives

“…Thus, the combination of aza‐Wittig and Wolff rearrangements was successfully utilized for the cyclization of 2‐ethynyl‐ N ‐triphenylphosphoranylidene anilines and α‐diazoketones leading to 5 H ‐benzo[ b ]carbazoles 36 (Scheme 19). [62] The authors employed only reflux in DCE or xylene as the reaction conditions to obtain good yields of carbazoles. The reaction mechanism proposed consists in a Wolff rearrangement of the diazo ketone giving a ketene intermediate, followed by an aza‐Wittig reaction with phosphorane, a biradical cyclization, and a 1,5‐H shift (Scheme 19).…”

Dearomatization–Rearomatization Strategy for Synthesizing Carbazoles with 2,2′-Biphenols and Ammonia by Dual C(Ar)–OH Bond Cleavages

“…Traditionally, Fischer–Borsche reaction is the main method to synthesize carbazole compounds, , but the process requires multiple steps, including condensation, cyclization, and dehydrogenation. Subsequently, a one-pot C–C and C–N bond bond-forming coupling reaction was used to synthesize carbazole derivatives. − In recent years, indole as a readily available raw material provided an opportunity for the synthesis of carbazoles. − More recently, intramolecular C–H amination was reported to construct carbazoles . Very recently, the conversion of 1,1′-bi-2-naphthol into 7 H -dibenzo­[c,g]­carbazole was reported by Ito and Kawamoto’s group with prolonged heating at 200 °C. , …”

Gold(I)-Catalyzed Formal Intramolecular Dehydro-Diels–Alder Reaction of Ynamide-ynes: Synthesis of Functionalized Benzo[b]carbazoles

“…Benzo­[ b ]­carbazoles, including aryl- and heteroaryl­[ b ]­carbazoles, are an important class of nitrogen-containing heterocyclic compounds, which have been found in a wide variety of biologically active substances and have also received much attention in the fields of organic functional materials as fluorescent chemosensors, organic light-emitting diodes (OLEDs), and organic field effect transistors (OFETs) . For instance, ellipticine A and its analogues have been intensively studied over the past 50 years because of their anticancer properties .…”

“…These compounds have been commonly prepared from substituted indoles or naphthalenes . Recently, a number of synthetic approaches to benzo­[ b ]­carbazoles have been reported ,, such as intramolecular dehydro-Diels–Alder reaction of ynamides, − biradical cyclization of N -(2-alkynyl­phenyl)­ketenimines, , radical cyclization through imidoyl selanide intermediates, Pd-catalyzed cyclization of 2-alkynyl­benzaldehydes with indoles, iron-catalyzed isomerization/cyclodehydration of 2-[(indoline-3-ylidene)­(methyl)]­benzaldehyde derivatives, etc. However, these methods usually have some limitations such as harsh conditions, being restricted to special substituted substrates, lack of flexibility, low product yields, etc.…”