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

TL;DR

A new rhodium-catalyzed method efficiently creates indazole-fused pyran compounds with tunable fluorescence.

Contribution

A regioselective Rh(III)-catalyzed [4+2] annulation method for synthesizing indazole-fused pyrans is introduced.

Findings

The dual directing groups enable selective C7–H activation over C5–H.

The method allows synthesis of structurally diverse indazole-fused pyran derivatives under mild conditions.

The compounds show tunable fluorescence and solvatochromic behavior.

Abstract

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.

Figures