An Expedient Ruthenium(II) Catalyzed Multicomponent Access to Phthalazinones Bearing Trisubstituted Alkenes

Nitrogen based heterocycles bearing trisubstituted alkenes are prodigious and indispensable motifs in pharmaceuticals, clinical candidates and functional materials. Herein, we developed a tandem one-pot ruthenium-catalyzed multicomponent reaction to access phthalazinones bearing trisubstituted alkenes by employing readily available hydrazines, 2-formyl-benzoic acid and alkynes. The key highlights of this work are its atom economy and greenness, with water as the only byproduct. This reaction exhibits high functional group tolerance and is also scalable to gram-scale synthesis. Remarkably, the current protocol is applied to a four-component reaction involving in situ nitro reduction by utilizing TFE (2,2,2-trifluoroethanol) as a liquid hydrogen carrier, along with imine formation and esterification. A series of control experiments were conducted to elucidate the reaction mechanism. Importantly, the possible intermediates were confirmed by mass spectrometry. Moreover, the products obtained show strong emission properties that are aligning well with DFT calculations.