Synthesis and Photophysical Properties of 3-Substituted-1 H -Indazoles: A Pd-Catalyzed Double C-N Bond Formation Strategy via 1,6-Conjugate Addition.

A Pd-catalyzed cascade process for the direct synthesis of 3-substituted-1 H -indazole employing p -quinone methide ( p -QM) and arylhydrazine through Pd-catalyzed double C-N bond formation via 1,6-conjugate addition is reported. This reaction strategy affords efficient and practical access to synthetically important diverse 3-substituted-1 H -indazoles in good yields. The photophysical properties of the synthesized 3-substituted-1 H -indazoles are investigated, and some of them showed very good fluorescence properties with quantum yields up to 85%. Also, the synthesized 3-substituted-1 H -indazole exhibits an acid-sensitive fluorescence turn-off activity.