C–H Halogenation of Pyridyl Sulfides Avoiding the Sulfur Oxidation: A Direct Catalytic Access to Sulfanyl Polyhalides and Polyaromatics

摘要

Palladium-catalyzed oxidative C–H halogenation and acetoxylation reactions of S-unprotected sulfides, selectively directed by pyridinyl groups, allows the formation of C–X bonds (X = I, Br, Cl, OAc) by using simple halosuccinimide or phenyliodine diacetate (PIDA) oxidants. The undesired formation of sulfoxides and/or sulfones, which are usually observed under oxidative conditions, is fully obviated. Under the solvent-dependent conditions that we proposed, sulfide C–H functionalization is achieved in less than 1 h without any direct electrophilic halogenation at the pyridine moiety. N-Directed ortho-C–H activation of aryl also facilitates dibromination reactions which are hardly accessible with sulfone and sulfoxide counterparts because of their higher structural rigidity. This general method gives a straightforward access to polyhalide sulfides, without an organosulfur reduction step or protection–deprotection sequence. Polyhalide sulfides are valuable synthons that give a practical entry to new constrained polyaromatic and biphenyl sulfides, including synthetically challenging unsymmetrical examples.