Visible-Light-Promoted Intramolecular Annulation of 2-Alkynylbiphenyl Compounds to Synthesize 9-Sulfenylphenanthrenes Under Metal-Free and Additive-Free Conditions

A convenient and environmentally friendly visible-light-promoted annulation reaction of 2-alkynylbiphenyls with diaryldisulfide for the synthesis of 9-sulfenylphenanthrenes bearing a sulfur-containing functional group has been developed. This mild and efficient approach was achieved through continuous irradiation with visible light under metal-free and additive-free conditions. A range of 9-sulfenylphenanthrene products were prepared in moderate to good yields with a broad scope and functional group tolerance.