An overview of palladium‐catalyzed synthesis of seven‐membered heterocycles

Abstract

Heterocyclic compounds are the ones that have always remained in the limelight owing to their superior contributions toward various disciplines such as biology, medicine, material science, pharmaceutical science, industry and so on. They form the building blocks of DNA and RNA macromolecules. Suitable tuning of these heterocyclic compounds can result in chemotherapeutic moieties with superlative efficiency. Seven‐membered heterocyclic compounds are an important class of heterocyclic chemistry. Some of them are azepine, oxepine, thiepine, diazepine, thiazepine and so on. Transition metal‐catalyzed synthesis of heterocycles has been the most explored in the recent past. Palladium is known as the best suitable catalyst for the same and that is the result of its excellent functional group tolerance and catalytic potency. Here, we intend to summarize the various investigations made on the palladium‐catalyzed synthesis of seven‐membered heterocycles. To the best of our knowledge, this is the first review in this topic and covers literature up to 2020.

Facile Synthesis of S‐Fused Multi‐Membered Polycyclic Heterocycles: A Construction Strategy towards Thermally Stable Thiepine Derivatives

“…[ 10 ] Therefore, thiopyran‐ and thiepine‐based heterocycles demonstrate completely different electronic structures and properties as compared with thiophene derivatives. In the past decades, they have been exploited in the fields of medicine, [ 11 ] agricultural pharmacology, [ 12 ] and organic functional materials. [ 13 ] However, in contrast to the abundant synthetic methodologies towards the construction of thiophene‐ fused heteroarenes, [ 14 ] the synthesis of the polycyclic heterocycles containing six‐membered thiopyran and seven‐membered thiepine is much less reported probably owing to their unfavorable…”

Effects of the Solvent and the Nucleophile on the Photochemical Synthesis of Azepines

“…These include metalcatalyzed cycloaddition reactions of alkynes to aminoketones, nitriles, and alkyl azides. [6][7][8][9][10][11][12] In contrast to the metal catalysis strategy, photochemical methods using easily synthesizable substrates have been introduced. These aim to expand the benzene ring during the intramolecular rearrangement of aryl nitrenes or the addition of carbenes to pyridines.…”

“…Often, these approaches depend on the use of transition metal catalysts, with a careful selection of substrates and reaction conditions. These include metal‐catalyzed cycloaddition reactions of alkynes to aminoketones, nitriles, and alkyl azides [6–12] …”

Stereoselective [4+3]-Cycloaddition of 2-Amino-β-nitrostyrenes with Azaoxyallyl Cations to Access Functionalized 1,4-Benzodiazepin-3-ones

“…Indeed, the effective synthesis of a wide range of functionally diverse 1,4-benzodiazepinone derivatives has garnered considerable research attention [ 4 , 13 , 14 , 15 , 16 , 17 ]. However, the synthesis of a seven-membered ring 1,4-benzodiazepinone presents difficulties due to unfavorable enthalpic and entropic factors that hinder the ring closure process [ 18 ].…”