Regioselective [3+2]‐Spiroannulation and [4+n]‐Annulation Approaches through Activation of C−H Bond Facilitated by Ru(II) as Catalyst: Role of Solvent Selectivity

Abstract Ru(II)‐catalyzed and solvent‐switched [3+2]‐spiroannulation and [4+n] (n=1, 2, 3) annulations of 2‐aryl quinazolinone or 2‐aryl‐2,3‐dihydrophthalazine‐1,4‐diones with ynones or alkynyl alcohol or 1,3‐diynes under mild reaction conditions have been analyzed. These reactions take place in the presence of the appropriate solvent and features a redox‐neutral pathway. Ynone serves as an ‘atypical one‐carbon unit’ in [4+1] annulation and generates a tetrasubstituted carbon center bearing diverse heterocycles through [3+2] and [4+1] annulation strategies. Post transformations of the synthesized spiro‐products augments the potential of the developed methodology.