Palladium-catalysed direct heteroarylation of bromobenzenes bearing SO₂R substituents at C2 or C4

Abstract

Palladium-catalysed direct arylation of 4- or 2-bromobenzenesulfonic acid derivatives in the presence of a variety of heteroaromatics was found to proceed using 0.1–0.5 mol% palladium acetate as the catalyst. However, both the nature and position of the SO₂R substituent on such bromobenzenes has an influence on the reaction rates and yields. The presence of SO₂Et or SO₂NEt₂ at the C2 or C4 position of bromobenzene is tolerated. Good results were also obtained from bromobenzene substituted at C4 by SO₂NHPh or SO₂OPh. On the other hand, the reactions of bromobenzenes bearing either SO₂N(Me)CH₂Ph or SO₂OAr at C2 led in some cases to intramolecular reactions instead of the desired intermolecular couplings. Some reactions were performed in cyclopentyl methyl ether, which can be considered as a green solvent.