C‐N and N‐N bond formation via Reductive Cyclization: Progress in Cadogan /Cadogan‐Sundberg Reactionǂ

Abstract

Cadogan/Cadogan‐Sundberg cyclization reaction has been reported as one of the most efficient routes for the synthesis of a wide variety of N‐heterocycles from the easily accessible starting materials such as o‐nitrobiaryls or o‐nitroarenes, o‐nitrostyrenes by treating with tetravalent phosphorus compounds (trialkyl or triaryl phosphines or trialkyl phosphites). The reaction has been successfully employed in Carbon‐Carbon as well as Carbon‐Nitrogen bond formation for the scaffolds like carbazole, indoles, coumarins, and indazoles. To the best of authors’ knowledge, the present review is the first compilation of the literature from almost two decades (2000 to present) on Cadogan/Cadogan‐Sundberg cyclization reaction, its scope, mechanistic aspects, and limitations.

Synthesis and characterization of S,N-heterotetracenes

“…Synthesis of S,N -heterotetracene H -SN4 13 and related derivatives by Cadogan reaction of nitro-substituted precursors . Another possibility for the preparation of fused pyrrole rings is established by the Cadogan reaction [ 40 ]. Well-known examples are the reductive cyclization of 2-nitro-1,1’-biphenyls with triethyl phosphite or phosphanes as reducing agent to provide carbazoles covering a wide substrate and functional group spectrum [ 41 ].…”

Electrochemical Reductive Arylation of Nitroarenes with Arylboronic Acids

“…Based on the mechanism research experiments and literature investigations, [14b,15,20] a possible mechanism for this electrochemical reductive arylation of arylboronic acids with nitroarenes is proposed in Scheme 6. Two possible mechanism paths are proposed.…”

Synthesis of indole derivatives as prevalent moieties present in selected alkaloids

“…313,314 Among the ergot alkaloids (EAs) family of naturally occurring compounds, lysergic acid 315 is the most broadly identied member and various semisynthetic derivatives have been clinically utilized for treating various neurological diseases. In 2015, Boger et al demonstrated 316 that the total synthesis of dihydrolysergic acid (363) and dihydrolysergol (364) relied on a palladium (0)-mediated intramolecular Larock indole cyclization for the formation of the tricyclic indole and also a consequently inverse electron demand Diels-Alder reaction. The total synthesis of dihydrolysergic acid (363) and dihydrolysergol (364) were commenced from 2-bromoaniline (359).…”

“…In 2015, Boger et al demonstrated 316 that the total synthesis of dihydrolysergic acid (363) and dihydrolysergol (364) relied on a palladium (0)-mediated intramolecular Larock indole cyclization for the formation of the tricyclic indole and also a consequently inverse electron demand Diels-Alder reaction. The total synthesis of dihydrolysergic acid (363) and dihydrolysergol (364) were commenced from 2-bromoaniline (359). The latter, aer ve steps, gave homopropargylic alcohol 360, that through an intramolecular palladium(0)-mediated Larock indole annulation gave the tricyclic indole 361.…”

“…The reaction of methyl 2-nitrophenylacetic acid (434) with formaldehyde (HCHO), tetrabutylammonium iodide ( n -Bu 4 NI) and K 2 CO 3 in toluene provided 2-(2-nitrophenyl)acrylate (435) in a good yield (85% yield). Then, phytoalexin (437) was synthesized in a good yield (85%) from 435 using modified Cadogan–Sundberg conditions, 364 for instance, using trimethylphosphite (P(OCH 3 ) 3 ) instead of triethylphosphite (P(OEt) 3 ).…”