Synthesis of Naphtho-Fused Imidazo[1,2-a]pyridines through Copper-Catalyzed Cascade Reactions

A highly efficient copper-catalyzed one-pot tandem protocol has been developed for the synthesis of naphtho-fused imidazo[1,2-a]pyridines. The transformation involves a Knoevenagel condensation followed by a chemoselective cross-coupling reaction along with a carbon-carbon bond cleavage. This protocol can tolerate a variety of functional groups and provided naphtho[1',2':4,5]imidazo[1,2-a]pyridines in moderate to excellent (35-91%) yields. The photophysical studies of the naphtho-fused imidazo[1,2-a]pyridines show a bathochromic shift between the band maxima of the absorption and emission spectra. These compounds emit with high fluorescence quantum yields.