Application of 2-(2-chloroaroyl)methyleneimidazolidines in domino and multicomponent reaction: new entries to imidazo[1,2-a]pyridines and benzo[b]imidazo[1,2,3-ij][1,8]naphthyridines

A new strategy for the synthesis of tetrahydroimidazo[1,2-a]pyridines and unusual tetrahydrobenzo[b]imidazo[1,2,3-ij][1,8]naphthyridines has been successfully developed by cascade reactions including Knoevenagel condensation, aza–ene reaction, imine–enamine tautomerization, cyclocondensation/oxidation, and intramolecular SNAr of precursors 2-(2-chloroaroyl)methyleneimidazolidines as new heterocyclic ketene aminals (HKA), which represent a class of polyfunctional scaffolds with four active reaction sites with aromatic aldehydes and malononitrile or ethyl 2-cyanoacetate under mild conditions. In this domino reaction, nine different active sites are involved, and two C–C bonds, two C–N bonds, and two new rings are constructed with all reactants efficiently utilized in the chemical transformation.

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