Intramolecular cyclization reaction — Palladium(0)-catalyzed cyclization is more effective than tin hydride mediated reaction

Abstract

Intramolecular CH arylation of pyrone, pyridone, uracil, imidazole, and benzimidazole derivatives are carried out in the presence of a Pd catalyst to form potentially bioactive fused heterocyclic compounds, whereas the n-Bu3SnH-mediated aryl radical cyclization of the precursors 3 afforded mainly halogen-reduced uncyclized products.Key words: Pd(0) catalyst, CH arylation, intramolecular cyclization, regioselectivity.

Access to Aromatic Ring-Fused Benzimidazoles Using Photochemical Substitutions of the Benzimidazol-2-yl Radical

“…Alternatively nonradical palladium-catalyzed cyclizations from aryl or imidazole halides to give aryl ring-fused diazoles in higher yields have been reported. 15,16 However, we were interested in accomplishing these annulations without metal catalysts or chemical initiators given that our group had previously reported UVmediated six-and seven-membered cyclizations from 2-iodo-1-(2-phenylethyl)-1H-imidazole and 2-iodo-1-(3-phenylpropyl)-1H-imidazole to give 5,6-dihydroimidazo[2,1-a]isoquinoline and 6,7-dihydro-5H-imidazo[2,1-a] [2]benzazepine in 70 and 48% yield respectively. 6 The present article details the photochemical conditions required in order to achieve optimized five-, six-, and sevenmembered homolytic aromatic substitutions of the benzimidazol-2-yl radical.…”

Pd/Pivalic Acid Mediated Direct Arylation of 2‐Pyrones and Related Heterocycles

“…[37] This compound could not be fully separated from the residual starting material by chromatographic methods. [37] This compound could not be fully separated from the residual starting material by chromatographic methods.…”

“…[32] 2-Quinolones also have a prominent biological profile, [33] such as the antihistamine Repirinast ( Figure 1). Previous cyclisations by Majumbar [37,38] and us, [39] using so-called Jeffrey's conditions, require the use of stoichiometric or superstoichiometric amounts of TBAB and thus suffer from poor atom and cost economy, falter from an environmental viewpoint (halide waste) and would be avoided by the pharmaceutical industry. Development to include to these substrates would greatly improve the widespread usability of any protocol.…”

Intermolecular versus Intramolecular Palladium‐Catalyzed Direct Arylations between 1‐(2‐Bromobenzyl)imidazoles and Aryl Bromides

“…[4a,e,f, 6] In 2014, Laha and co-workers reported aone pot procedure,i.e, N-benzylation/intramolecular C À Ha rylation for the synthesis of annulated nitrogen heterocycles from imidazole and 2-bromobenzyl bromide ( Figure 1c). [7] TheC -2 intramolecular direct arylation has also been performed using CuI associated with 1,10-phenanthroline as catalytic system (Fig-ure 1d).…”