Synthesis and Photophysical Properties of 5-N-Arylamino-4-methylthiazoles Obtained from Direct C–H Arylations and Buchwald–Hartwig Aminations of 4-Methylthiazole

Abstract

5-N-Arylamino-4-methylthiazoles were synthesized from commercially available 4-methylthiazole in three consecutive steps: (i) direct Pd-catalyzed C–H arylations of the thiazole, (ii) bromination, and (iii) Pd-catalyzed Buchwald–Hartwig aminations. The resulting thiazoles showed the longest-wavelength absorption maxima at 338–432 nm, and luminescence was observed at 455–726 nm, whereby the latter depends predominantly on the substituents at the 2-position of the thiazole core. The introduction of electron-accepting groups, in particular a nitro group, induced substantial bathochromic shifts of the fluorescence. Thiazoles containing a 3,5-bis(trifluoromethyl)phenyl group at the 2-position exhibited purple to blue emission in the solid state. The energy levels of the frontier molecular orbitals and the Kohn–Sham plots of the 5-N-arylamino-4-methylthiazoles were obtained from DFT calculations at the B3LYP/6-31+G(d,p) level of theory.