Modulating the reactivity of heterocyclic ketene aminals in MCR: selective construction of tetrahydrobenzo[b]imidazo[3,2,1-ij][1,8]naphthyridines.

Two new kinds of tetrahydrobenzo[b]imidazo[3,2,1-ij][1,8]naphthyridine derivatives have been successfully synthesized by cascade reactions including Knoevenagel condensation, aza-ene reaction, imine-enamine tautomerization, cyclocondensation, and intramolecular S(N)Ar of precursors 2-(2-chloroaroyl)methyleneimidazolidines with aromatic aldehydes and ethyl acetoacetate or Meldrum's acid under mild conditions, respectively. These studies highlighted the concept of a substrate-design approach to the development of novel multicomponent reactions by simply incorporating an o-halo group into the aryl ring of 2-benzoylmethyleneimidazolidine as new synthons. In this domino reaction, at least six different active sites are involved; two C-C bonds, two C-N bonds, and two new rings are constructed with all reactants efficiently utilized in the chemical transformation.