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

Abstract

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-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 bond activation processes can compete with the usually fast syn beta-hydrogen elimination step in the Heck arylation of an acyclic olefin. The structural scope of this palladium-catalyzed cascade arylation of alpha,beta-unsaturated sulfones has proved to be wide with regard to substitution at the beta-position (alkyl, aryl, or alkenyl substitution), substitution at the sulfone unit (alkyl or phenyl sulfones), and configuration at the CdoublebondC bond (trans or cis). Moreover, although less favored than in the case of the arylation of alpha,beta-unsaturated sulfones, similarly substituted 9,10-dihydrophenanthrenes have also been obtained in the case of alpha,beta-unsaturated phosphine oxides and alpha,beta-unsaturated phosphonate esters. A Pd(0)-Pd(II)-Pd(IV) mechanistic pathway involving the successive formation of highly electrophilic sigma-alkylpalladium intermediates and palladacycles is proposed for this multicomponent arylation.

Catalytic C–C coupling through C–H arylation of arenes or heteroarenes

“…intramolecular aromatic C-H activation process with formation of the five-membered palladacycle (Scheme 35) [119].…”

The first nucleophilic substitution reaction of organoindium reagents with sulfonyl chlorides: a facile method for preparation of vinyl sulfones

“…Especially, no desired reaction took place in benzene (entry 8 in Table 1). We could deduce no formation of vinylindium in benzene, as quenching with saturated NH 4 Cl previous to adding TsCl did not give styrene under the same conditions. Presumably, this reaction was a vinylindium formation-controlled process.…”

“…For example, the chemical versatility of the sulfone moiety enable these compounds to undergo highly stereoselective nucleophilic conjugate additions and cycloadditions, 1 cyclopropanation, 2 epoxidation, 3 palladium-catalyzed cascade arylation with aryl iodides, 4 radical conjugate additions, 5 and aza-Michael addition. 6 Vinyl sulfones have been used for total synthesis of natural products.…”

Bibliographical Background: The Ortho Effect in The Catellani Reaction

“…Thus dihydrophenanthrene 34 could be synthesized from iodobenzene and vinyl sulfone 33 in the presence of Pd(OAc) 2 and Ag 2 CO 3 ( Fig. 7.12) [43]. Vinyl sulfones and a,b-unsaturated phosphine oxides are the only non-strained olefins to allow this kind of reaction.…”