Palladium-Catalyzed C–H Bond Direct Alkynylation of 5-Membered Heteroarenes: A Well-Defined Synthetic Route to Azole Derivatives Containing Two Different Alkynyl Groups

Abstract

A widely applicable oxidative coupling of 5-membered heteroarenes and terminal alkynes that uses a combination of palladium and silver salts was developed. Under suitable conditions, imidazole and benzimidazole, which are sluggish under similar previously reported oxidative coupling conditions, as well as imidazo[1,5-a]pyridines, oxazole, benzoxazole, thiazole, and benzothiazole could be alkynylated. In addition, the bromine atom on the substrates was intact under the reaction conditions, and conventional Sonogashira coupling did not occur at all. With these reactivities in hand, a well-defined synthetic route to imidazo[1,5-a]pyridines and thiazole containing two different alkynyl groups was achieved in a simple manner. In addition, linear correlations were observed between the fluorescence wavelength and the Hammett substituent constants of aryl groups, not only on the C1- but also on the C3-alkynyl group of the obtained 1,3-bis(arylethynyl)imidazo [1,5-a]pyridines.

Direct CH Arylation of Heteroarenes Catalyzed by Palladium/ Nitrogen‐Based Ligand Complexes

“…We also reported a direct oxidative alkynylation of azoles with a Pd complex 41 /Ag 2 CO 3 system (Scheme ) 10g. Usually, such direct oxidative alkynylation only proceeds at acidic CH bonds, and the reaction does not occur at relatively less acidic CH bonds, such as the C2 position of imidazoles.…”

Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters

“…The challenging synthetic task in this work resides in the introduction of an ethynyl substituent at the 2-position of the benzochalcogenazole ring. Whereas af ew examples of ethynyl-bearing benzoxazole and -thiazole derivatives have been described so far, [38][39][40][41][42][43][44][45][46][47][48][49][50] no reports are known on the synthesis of ethynyl-derivatised benzoselenazole and -tellurazoles. Depending on the chalcogenic atom, three different synthetic strategies have been envisagedt op repared erivatives 1 X and 2 X (Scheme 1).…”

Synthesis of Dimeric Imidazo[1, 5‐a]pyridines and Their Photophysical Properties

“…We examined the synthesis of 1,1’‐diaryl‐3,3’‐biimidazo[1, 5‐ a ]pyridines 2 from commercially available imidazo[1, 5‐ a ]pyridine in three steps involving bromination at C 3 ‐position, Suzuki‐Miyaura cross coupling, and dimerization (Scheme ). According to a literature precedure, 1‐bromoimidazo[1, 5‐ a ]pyridine was prepared by the reaction of commercially available imidazo[1, 5‐ a ]pyridine with N ‐bromosuccinimide …”