One-pot approach to the synthesis of novel 12H-chromeno[2′,3′:4,5]imidazo[1,2-a]pyridines in aqueous media

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

The sequential three-component reaction between o-hydroxybenzaldehydes, N-(cyanomethyl)pyridinium salts and a nucleophile towards substituted chromenoimidazopyridines under oxidative conditions has been developed. The employment of Mn(OAc)₃·2H₂O or KMnO₄ as stoichiometric oxidants allowed the use of a wide range of nucleophiles, such as nitromethane, (aza)indoles, pyrroles, phenols, pyrazole, indazole and diethyl malonate. The formation of the target compounds presumably proceeds through a domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction sequence.

One-Pot Tandem Amidation, Knoevenagel Condensation, and Palladium-Catalyzed Wacker Type Oxidation/C-O Coupling: Synthesis of Chromeno-Annulated Imidazopyridines

A direct one-pot synthesis of chromeno-annulated imidazo[1,2- a]pyridines is achieved by the reaction of 2-amino-1-(2-ethoxy-2-oxoethyl)pyridinium salts with 2-bromoarylaldehydes using Pd(TFA)₂ as a catalyst and Cu(OAc)₂ as an oxidant. The overall strategy involves tandem base-mediated amidation and Knoevenagel condensation, followed by palladium-catalyzed Wacker type oxidation and intramolecular C-O coupling reaction. The method is simple, tolerates different functional groups, and gives moderate to good yields of chromeno[2',3':4,5]imidazo[1,2- a]pyridin-12-one derivatives. The developed tandem reaction was also successfully applied for the synthesis of pyrano-fused imidazo[1,2- a]pyridines by using 3-bromo-3-arylacrylaldehydes.

Synthesis of fused cyanopyrroles and spirocyclopropanes via addition of N-ylides to chalconimines

DABCO-ylides react as a one-carbon source with chalconimines to afford fused cyanopyrrolesvia[4 + 1] annulation and spirocyclopropanesvia[2 + 1] annulation.

Domino reaction of N-(cyanomethyl)-1,3-azolium quaternary salts with o-hydroxybenzaldehydes: scope and limitations

A route towards chromenes, annulated with an imidazo[5,1-c][1,4]thiazine core through a base-promoted domino reaction of thiazolium quaternary salts, has been developed.