Synthesis of Nitrogen-containing Heterocyclic Compounds by Ring Enlargement Reactions through Bicyclic Cyclopropane Intermediates (Review)

Abstract

Papers on the synthesis of nitrogen-containing heterocyclic compounds by ring enlargement reactions based on the formation of an annelated cyclopropane ring by intramolecular alkylation followed by cleavage of the zero bridge in the obtained [n.1.0] bicyclic systems are reviewed.Ring enlargement is currently one of the most important and often the only tool for the synthesis of various carbocyclic and heterocyclic compounds [1-6]. A significant place among this type of transformations is occupied by reactions that proceed through small ring intermediates, in particular cyclopropanes [7][8][9][10][11][12][13]. Cyclopropanation of cyclic compounds followed by cleavage of the zero bridge in the obtained [n.1.0] bicyclic systems should be noted among the known synthetic strategies based on ring enlargement by one carbon atom. One of the methods for creating an annelated cyclopropane ring is intramolecular alkylation.This review is devoted to analysis of published data on the synthesis of nitrogen-containing heterocyclic compounds using the above-mentioned methodology. Synthesis of AzepinesThe most studied types of heterolytic cyclopropanation used for the construction of [n.1.0] bicyclic systems are intramolecular alkylation of enamines and related compounds of the X-(C=C) n -C-C-LG type, where X is an atom with a lone pair of electrons (e.g., N, N -, C -, etc.) and LG is a leaving group. Typical examples of these compounds are the readily available 1,4-dihydropyridines [14, 15] containing a halomethyl

Photochemical Skeletal Editing of Pyridines to Bicyclic Pyrazolines and Pyrazoles

“…Pyridine skeletal editing transformations can be categorized into two strategies: ring expansion and ring contraction (Figure D). Typically, the nucleophilicity of the nitrogen atom of pyridines is harnessed to prepare cationic pyridinium salts. − Pyridine expansion via N-functionalized pyridinium salt (imidopyridine ylide) has been widely employed in synthetic methodologies. − Additionally, ring contractions via carbon deletion under light or electricity have been documented, yielding pyrroles or pyrazolines as exclusive products. − …”

Synthesis, Characterization and Biological Screening of Azepine Derivative: 2-hydroxy-1,3-di(naphthalene-2-yl)-1H-benzo[b]azepine-5(4H)one

“…Azepine is an unsaturated heterocyclic organic compound of seven atoms, with nitrogen replacing a carbon at one position. Its chemical formula is C 6 H 7 N and its molar mass is 93.13 gmol -1 [1]. Azepine is a seven-membered nitrogen heterocycle with a biologically active epitope and a useful building block in the construction of various organic molecules.…”

Iodine-Mediated Pyridine Ring Expansion for the Construction of Azepines

“…Owing to the vital function of the azepine moiety in biologically active species, a number of methodologies have been developed for the synthesis of azepine-containing heterocycles. Most successful examples have been attributed to the photolysis of aryl azides (Scheme a), the alkylation of 1,4-dihydropyridines (Scheme b), the cycloaddition of bifunctional nitrogenous compounds (Scheme c), the intermolecular [3 + 2 + 2]/[4 + 3]/[5 + 2] cycloaddition of aziridines with alkynes (Scheme d), and the ring enlargement of pyridines/quinolines (Scheme e). , …”

“…For example, phenyl azides were dangerous chemicals with explosion hazardous characteristics (Scheme a) . The substrates shown in Scheme b were restricted to 1,4-dihydropyridine bearing two electron-withdrawing groups at the 3,5-positions and one halogenated methyl group at the 4-position of the pyridine ring . The substrates in Scheme c–e were limited to a few noncommercially available compounds endowed with specific structures.…”