Palladium‐Catalyzed Cascade Reaction of α,β‐Unsaturated Sulfones with Aryl Iodides

Abstract Unlike traditionally used acyclic 1,2‐disubstituted alkenes, the reaction of α,β‐unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions (Pd(OAc) 2 as catalyst, Ag 2 CO 3 as base in DMF at 120 0 C) takes place mainly by a cascade process, involving one unit of the alkene and three units of the aryl iodide, to afford a substituted 9‐phenylsulfonyl‐9,10‐dihydrophenanthrene. The dominant formation of this 3:1 coupling product, instead of the Heck trisubstituted olefin, shows that aromatic CH activation processes can compete with the usually fast syn β‐hydrogen elimination step in the Heck arylation of an acyclic olefin. The structural scope of this palladium‐catalyzed cascade arylation of α,β‐unsaturated sulfones has proved to be wide with regard to substitution at the β‐position (alkyl, aryl, or alkenyl substitution), substitution at the sulfone unit (alkyl or phenyl sulfones), and configuration at the CC bond ( trans or cis ). Moreover, although less favored than in the case of the arylation of α,β‐unsaturated sulfones, similarly substituted 9,10‐dihydrophenanthrenes have also been obtained in the case of α,β‐unsaturated phosphine oxides and α,β‐unsaturated phosphonate esters. A Pd 0 –Pd II –Pd IV mechanistic pathway involving the successive formation of highly electrophilic σ‐alkylpalladium intermediates and palladacycles is proposed for this multicomponent arylation.