Visible light–mediated, rose Bengal–catalyzed oxidative radical C-H cyclization of alkyl 1,1’-biaryl-2-ones: An efficient synthesis of 10-alkylphenanthren-9-ols in water

Abstract A visible light-mediated (blue LED: λ= 455±10 nm), rose bengal-catalyzed intramolecular cycloaromatization reaction of alkyl 1, 1’-biaryl-2-ones for the synthesis of 10-alkylphenanthren-9-ols in water under open air atmosphere at ambient conditions has been developed. Experimental studies demonstrate that the reaction proceeded via a radical pathway. This protocol is applicable to a wide variety of substrates giving expected 10-alkylphenanthren-9-ols in good yields, appropriate for the gram-scale synthesis, atom economy, and eco-friendly as compared to literature reported methodology for the preparation of phenanthrol derivatives. Moreover, to the best of our knowledge, no instance has hitherto been accounted on the visible light-induced transformation of readily available alkyl 1,1’-biaryl-2-ones to 10-alkylphenanthren-9-ols.