Coordination Assisted Distal C−H Alkylation of Fused Heterocycles

Abstract

Distal C À Hb ond functionalization of heterocycles remained extremely challenging with covalently attached directing groups (DG). Lackofproper site for DG attachment and inherent catalyst poisoning by heterocycles demand alternate routes for site selective functionalization of their distal CÀHb onds.U tilizing non-productive coordinating property to hold the heterocycle into the cavity of at emplate system in ahost-guest manner,wereport distal C À Halkylation (C-5 of quinoline and thiazole,C -7 of benzothiazole and benzoxazole) of heterocycles.U pon complexation with heterocyclic substrate,n itrile DG in template directs the metal catalyst towards close vicinity of the specific distal CÀHb ond of the heterocycles.O ur hypothesized pathway has been supported by various X-ray crystallographically characterized intermediates.

Coordination Assisted Distal C−H Alkylation of Fused Heterocycles

“…TheC5selectivity has been further confirmed by the X-ray crystallography structure [16] of 3b. Va rious substituted quinolines, irrespective of the position of substitution, are found to be compatible with the present strategy (Scheme 2).…”

“…In order to get insights into the reaction mechanism, several intermediates have been characterized by X-ray crystallography [16] and other spectroscopic techniques. Based on these evidences,aplausible mechanistic pathway has been put forward (Scheme 5).…”

Beyond hydrogen bonding: recent trends of outer sphere interactions in transition metal catalysis

“…This time, the reaction was enabled by a C 1 -symmetric template (Scheme 40). 170 All these regio-selectivities cannot be achieved with ligands or templates lacking the well-designed recognition site within the second coordination sphere. Such level of sophistication was upgraded by merging this template strategy with the Catellani reaction, which consists in employing a Pd/norbornene catalytic system to functionalize one C-H bond away from the first C-H bond activation.…”

“…Furthermore, it is possible to recycle and recover the template by treatment with 4dimethylaminopyridine, which coordinates stronger to the palladium template than the substrates and the products, followed by a mild acidification. [167][168][169][170][171] It is relevant to note that the success of these strategies relies also on the non-negligible roles of mono-protected amino acids co-ligands, silver salts and hexafluoroisopropanol as solvent.…”

Consecutive Oxidation/Condensation/Cyclization/Aromatization Sequences Catalyzed by Nanostructured Iron(III)‐Porphyrin Complex towards Benzoxazole Derivatives

“…Heterocycles are cyclic compounds composed of carbon, hydrogen, and heteroatom (including oxygen, or nitrogen, or both O and N) Benzoxazoles contain O and N heteroatoms and are a significant class of benzo‐fused heterocyclic products. Among diverse fused‐ring heterocyclic compounds, the benzoxazole scaffold broadly exists in numerous compounds with many and various biological activities including antibacterial, anticancer, anti‐measles virus and anti‐HIV activities , …”