Rh(III)-Catalyzed Regioselective [4 + 2] Annulation of 2-Benzyl-2H-indazole-6-carboxylic Acids with Ynamides to Access Indazole-Fused Pyrans.

We report a Rh (III)-catalyzed C7-H activation/[4 + 2] annulation of 2-benzyl-2H-indazole-6-carboxylic acids with ynamides, enabling the regioselective synthesis of indazole-fused pyrans. Mechanistic studies highlight the pivotal role of the dual directing groups (indazole and carboxylic acid) in facilitating selective C7-H bond activation, even in the presence of the competing C5-H bond. This method provides a straightforward and efficient approach for accessing structurally diverse indazole-fused pyran derivatives under mild reaction conditions. In the photoluminescence study, the synthesized compounds exhibited tunable fluorescence (410-520 nm), covering most of the visible spectrum, along with a positive solvatochromic shift in solvents of varying polarity.