Pd-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins and indoles: synthesis of benzofuran and indole fused heterocycles

Abstract

Palladium-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins provided the benzofuran fused transannulated products in good to excellent yields via decarbonylative approach. While imidazo[1,2-a]pyridines with N-methyl indoles in the presence of palladium...

A Comprehensive Review on Benzofuran Synthesis Featuring Innovative and Catalytic Strategies

“…In the same year, Semwal et al 73 proposed the palladium-promoted synthesis of benzofuran derivatives via ring formation reaction between imidazo[1,2- a ]pyridines 26 and coumarins 27 . They treated coumarins and imidazo[1,2- a ]pyridines by employing palladium acetate as a catalyst, Cu(OTf) 2 ·H 2 O as an oxidant, dimethylformamide as solvent, and 1,10-phenanthroline (as an excellent additive and catalyst) to procure benzofuran derivatives (by the removal of CO) in efficient yields ( Scheme 7 ).…”

Synthesis and site selective C–H functionalization of imidazo-[1,2-a]pyridines

“…The combination of K 2 CO 3 and 18-crown-6 was discovered to be the best option for this annulation reaction (Scheme 68). 132 Later, the same group also established a technique for the annulation of 2-arylimidazo[1,2- a ]pyridines with coumarin derivatives 162 in the presence of a palladium catalyst to furnish the annulated compounds 163 . All the annulated products were studied for their photophysical properties and exhibit fluorescence characteristics (Scheme 68).…”

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

“…38 Very recently a palladiumcatalyzed annulation reaction of imidazo[1,2-a]-pyridines with coumarins and indoles to give benzofuran and indole fused heterocycles has been reported by Adimurty (Scheme 1). 39 To address these reports and in continuation of our interest in the field of cross dehydrogenative coupling reactions, we wish to report a cross-coupling reaction between imidazo[1,2-a]pyridines with coumarin-3-carboxylic acids, which proceeds through a decarboxylative Michael addition to give arylimidazo-[1,2-a]pyridin-3-yl)chroman-2-ones (3). Gratifyingly, this process provided a route to dibenzoisochromenoimidazo[1,2-a]pyridin-6ones (4), possessing six fused rings, through a domino reaction containing Michael addition/decarboxylation/oxidation/annulation (Scheme 1).…”

“…38 Very recently a palladium-catalyzed annulation reaction of imidazo[1,2- a ]-pyridines with coumarins and indoles to give benzofuran and indole fused heterocycles has been reported by Adimurty (Scheme 1). 39…”