title: 1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines: synthesis, photophysical properties, and observation of a linear correlation between the fluorescent wavelength and Hammett substituent constants.
abstract: 1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines were synthesized. The Sonogashira coupling of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various terminal alkynes with Pd(PPh(3))(2)Cl(2) (10 mol %) and CuI (10 mol %) in triethylamine at 80 °C for 12 h afforded the corresponding 1-alkenyl-3-arylimidazo[1,5-a]pyridines in good to excellent yields. The Mizoroki-Heck reaction of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various styrene derivatives proceeded smoothly with Pd(OAc)(2) (5 mol %), IMes·HCl (10 mol %), and Cs(2)CO(3) (2 equiv) in DMA at 130 °C for 20 h to give the alkenylated imidazo[1,5-a]pyridines in moderate to high yields. The fluorescence maxima and fluorescence quantum yields of the alkynylated products were 458-560 nm and Φ(F) = 0.08-0.26 in chloroform solution, and those of the alkenylated imidazopyridines were 479-537 nm and Φ(F) = 0.03-0.13. The absorption behaviors of the obtained alkynylated and alkenylated imidazo[1,5-a]pyridines showed a good fit to the values predicted by TDDFT calculations at the B3LYP/6-311++G(d,p) level. In addition, the alkynylated imidazo[1,5-a]pyridines obtained showed linear correlations between the Hammett substituent constants of the substituents on the arylalkynyl group and their fluorescence wavelengths.
authors.affiliation: Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Yamaguchi
authors.forename: Fumitoshi
authors.initials: F
authors.lastname: Shibahara
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Murai
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry*; D000480:Alkynes / Q000138:chemical synthesis* / Q000737:chemistry; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
chemical_list: D000475:Alkenes; D000480:Alkynes; D007093:Imidazoles; D011725:Pyridines