Iodine-Catalyzed Methylthiolative Annulation of 2‑Alkynyl Biaryls with DMSO: A Metal-Free Approach to 9-Sulfenylphenanthrenes

An
iodine-catalyzed sustainable, cost-effective, and atom-economic
synthetic methodology is developed to synthesize a wide variety of
valuable sulfenylphenanthrenes and polycyclic heteroaromatics in moderate
to high yield through electrophilic thiolative annulation of 2-alkynyl
biaryls (6-endo-dig cyclization) using methyl sulfoxides
such as dimethyl sulfoxide (DMSO) as the sulfur source under transition-metal-free
conditions. The transformation requires only iodine in a catalytic
amount and trifluoroacetic anhydride. Notably, DMSO played multiple
roles such as methylthiolating reagent, oxidant, and solvent in this
reaction.