Substrate-Tuned Domino Annulation for Selective Synthesis of Poly-substituted Benzo[f]imidazo[2,1-a][2,7]naphthyridines and 3-Azaheterocyclic Substituted 2-Arylquinolines

Abstract

A domino annulation/oxidation of heterocyclic ketene aminals (HKAs) and 2-aminochalcones has been developed for the selective synthesis of poly-substituted benzo­[f]­imidazo­[2,1-a]­[2,7]­naphthyridines and 3-azaheterocyclic substituted 2-arylquinolines. These reactions proceed well under mild conditions without any additives. Plausible mechanisms for such a polycyclic ring system assembly were also proposed. Moreover, benzo­[f]­imidazo­[2,1-a]­[2,7]­naphthyridine 3g displayed a fluorescence effect, demonstrating the potential applications in organic optical materials.

Synthetic Access to α-Oxoketene Aminals by the Nucleophilic Addition of Enol Silane-Derived Palladium(II) Enolates to Carbodiimides

“…Consistent with numerous examples in the literature, the frequent deployment by contemporary organic chemists of α-oxoketene aminal intermediates as synthetic precursors to access a range of unique and complex heterocyclic compounds (e.g., pyrimidopyrrolopyridazines, benzo­[ f ]­imidazo­[2,1- a ]­[2,7]­naphthyridines, functionalized indoles, tetrahydroimidazo­[1,2- a ]­pyridines, spiro-oxindole, and 9-azabicyclo[3.3.1]­nonane derivatives) has rendered this motif as a versatile building block in organic synthesis. − α-Oxoketene aminal derivatives are most commonly prepared by the nucleophilic substitution of α-oxoketene dithioacetals with amines, as depicted by the representative example presented in Scheme , eq 1. − However, this specific methodology requires the preparation of α-oxoketene dithioacetal substrates that are typically obtained from ketone starting materials using CS 2 and a methylating agent (MeI or Me 2 SO 4 ) in the presence of a strong base (e.g., NaOH and NaH), a reaction protocol that has limited the potential for widespread application because of the use of toxic and/or volatile reagents . Alternatively, N , N ′-disubstituted ketene aminals can be derived from active methylene compounds (e.g., ethyl cyanoacetate) in a one-pot, two-step synthetic procedure involving treatment with NaH and an isothiocyanate to obtain an N , S -acetal intermediate, which is subsequently coupled with an amine in the presence of a thiocarbonyl activating reagent like EDCI (Scheme , eq 2) .…”

Microwave Irradiation and Formamide: A Perfect Match for Ultrafast Carbamoylation via Radical Reactions

“…Over the past decades, microwave irradiation has been extensively used in organic chemistry as a synthetic tool that fully adheres to the principles of green chemistry. − Among the environmentally benign processes for the synthesis of organic molecules, cascade reactions occupy a prominent place since they allow the formation of several bonds in one-pot protocols, have high atom economy, are facile to operate, and reduce the steps of workups, lowering the generation of waste. − Despite the advantages outlined above, radical cascade reactions triggered by microwave irradiation have scarcely been explored.…”