Base-mediated [4+2] annulation of electron-deficient nitrobenzoheterocycles and α,α-dicyanoalkenes in water: Facile access to structurally diverse functionalized dibenzoheterocyclic compounds

A base-mediated [4 + 2] annulation of 2-nitrobenzofurans, 2-nitrobenzothiophenes, 3-nitrobenzothiophenes, and 3-nitroindoles with α,α-dicyanoalkenes for the synthesis of structurally diverse dibenzoheterocyclic compounds was developed. The reaction proceeded smoothly via a tandem vinylogous Michael addition/cyclization/tautomerization/elimination process in water with cesium carbonate as base, affording a wide range of dibenzofurans, dibenzothiophenes and carbazoles in good to high yields. The synthetic potential of the methodology was demonstrated by the scale-up experiment and versatile transformations of the products. The optical property of the polyheterocyclic aromatic products was also preliminarily investigated.