Riboflavin Photocatalyzed Dearomative Spiro-Etherification of Naphthols

Atom-efficient chlorinative dearomatization of naphthol, quinolinol, and isoquinolinol derivatives using trichloroisocyanuric acid (TCCA)

A variety of dearomatized compounds have been prepared in moderate to excellent yields from planar scaffolds using trichloroisocyanuric acid (TCCA) as an atom-economical chlorinating agent. The method tolerates a broad range of functionalities and can take place in several green and/or sustainable solvents. Twenty-one examples of 1,1-dichlorinated products of dearomatized 2-naphthols and analogous heteroarenes (quinolinols, isoquinolinols, and quinazolinol) are reported along with five examples of monochlorinated dearomatized products. The utility of the 1,1-dichloronaphthalenone product as a reactive intermediate species is demonstrated in a two-step, one-pot reaction carried out in a green solvent. In a mechanistic investigation, the coordination of the chlorinating agent to the hydroxy substituent of the planar scaffold prior to chlorine transfer is implicated.

Metal- and base-free, aerobic photoredox catalysis with riboflavin to synthesize 2-substituted benzothiazoles

Sustainable approaches for the synthesis of 2-substituted benzothiazoles are sought after for their use in organic chemistry, bioorganic chemistry, and industrial applications. Here, we described a visible light-driven photoredox catalytic cyclization of thioanilides to afford 2-substituted benzothiazoles using riboflavin as a photocatalyst, where oxygen is used as a clean oxidant and ethanol as a greener solvent. These results provide a new photochemical route for environmentally benign synthesis.