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.

The Pd/Ag-mediated dropwise addition of terminal alkynes to various 5-membered azoles allows an easy access to a number of mono-and dialkynylated heteroarenes. -(SHIBAHARA*, F.; DOHKE, Y.; MURAI, T.; J. Org. Chem. 77 (2012) 12, 5381-5388, http://dx.doi.org/10.1021/jo3008385 ; Dep. Chem., Fac. Eng., Gifu Univ., Yanagido, Gifu 501-11, Japan; Eng.) -Jannicke 42-042