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