Reaction of imidazo[1,2-a]pyridines with coumarin-3-carboxylic acids: a domino Michael addition/decarboxylation/oxidation/annulation

Abstract

A palladium-catalyzed decarboxylative domino reaction of imidazo[1,2-a]pyridines and coumarin-3-carboxylic acids has been developed, which provides access to dibenzoisochromenoimidazo[1,2-a]pyridin-6-ones possessing six fused rings.

Recent Advances in the Decarboxylative Strategy of Coumarin‐3‐carboxylic Acid

“…In 2022, Kianmehr and co‐workers reported a facile, metal‐ and additive‐free C−C bond construction between imidazo[1,2‐a] pyridines 118 and coumarin‐3‐carboxylic acid 1 through a decarboxylative Michael addition to achieve an imidazo[1,2‐a]pyridin‐3‐yl‐chroman‐2‐one skeleton 119 (Scheme 28). [49] A domino reaction involving Michael addition/decarboxylation/oxidation/C−H bond activation and annulation has been carried out. The proposed mechanism for the reaction pathway says that the carboxylic acid group appears to bring the reactants nearer together by forming a hydrogen bond with the imidazo moiety, as well as increasing the electrophilicity of the olefinic part of coumarin for conjugate addition of imidazo[1,2‐a]pyridine to give intermediate 121 , which undergoes decarboxylation to form corresponding intermediate 122 .…”

Synthesis of Highly Substituted 1,2,4-Triazole-Based 3-Nitrochromanes through Aza-Michael Addition Reaction under Catalyst- and Base-Free Conditions

“…24 Also, the intermolecular aza-Michael addition reaction of nitrogen functionalities for the construction of 4-aminochromanes has been rarely reported. 25 From a literature survey, nitrogen-containing heterocyclics including indole, 26 pyrazole, 27 indazole, 28 imidazopyridine 29 and benzotriazole 30 act as prominent Michael donors and have taken part in Michael addition reactions. Among the various aza-heterocyclic systems, 1,2,4-triazoles are one of the most promising heterocyclic compounds exhibiting remarkable pharmacological activities including antibacterial, antiurease, antiviral, anticonvulsant, cannabinoid CB1 receptor antagonist, antimalarial and antioxidant properties, 31 and they are an essential constituent of all cells and living matter.…”

B(C6F5)3‐Catalysed Alkylation of Imidazo[1,2‐a]pyridines Using α,β‐Unsaturated Ketones

“…reported a catalyst‐free alkylation using β ‐nitrostyrenes (Scheme 1a) [23] . Carbon–carbon bond formation between imidazo[1,2‐ a ]pyridines and coumarin carboxylic acid has been achieved through a catalyst‐free decarboxylative Michael addition (Scheme 1b) [24] . Besides the catalyst‐free conjugate addition, Patel et al .…”

“…[23] Carboncarbon bond formation between imidazo[1,2-a]pyridines and coumarin carboxylic acid has been achieved through a catalystfree decarboxylative Michael addition (Scheme 1b). [24] Besides the catalyst-free conjugate addition, Patel et al reported the transition-metal catalysed reaction with maleimide using a manganese catalyst (Scheme 1c). [25] However, the alkylation of imidazo[1,2-a]pyridines using α,β-unsaturated ketones remains a challenge.…”