Unveiling the Three-Component Phosphonylation on Alkynylaldehydes: Toolbox toward Fluorescent Molecules.

A regioselective tandem approach for annulated napthyridines/isoquinolines embedded with the phosphine oxide group under mild reaction conditions has been achieved in good to excellent yields. The designed strategy involves the triflate-induced formation of new C sp-P and C sp-N bond formation in one pot. This protocol was also well tolerated for the construction of densely functionalized organo-phosphorylated chromenes in good yields. Further, phosphino-derived sulfamethazine and sulfamethoxazole drugs were also successfully synthesized in good yields. The mechanistic studies revealed that the ionic pathway and the formation of regioselective cyclized products were confirmed through X-ray crystallographic studies. Interestingly, photophysical studies of selectivity selected compounds revealed their stimulating fluorescence properties.