Palladium-catalyzed direct C5-arylation or C4,C5-diarylation of 2-alkylisothiazol-3-ones

Abstract

The regioselectivity of the Pd-catalyzed direct arylation of unsubstituted 2-alkylisothiazol-3(2H)-ones was investigated. Conditions for the regioselective palladium-catalyzed direct C5-arylation of 2-alkylisothiazol-3-ones using aryl bromides as the coupling partners are reported. This procedure tolerates a wide variety of substituents such as nitro, nitrile, ester, chloro, fluoro, trifluoromethyl, trifluoromethoxy, difluoromethoxy at para-, meta- and also ortho-positions on the aryl bromide. Both methyl- and octyl-substituents at 2-position of alkylisothiazol-3-ones are tolerated. Moreover, at a more elevated temperature in the presence of a larger excess of the aryl bromide, the access to the C4,C5-diarylated alkylisothiazol-3-ones is also possible, revealing that the C4-position of isothiazol-3(2H)-ones is reactive for direct arylation when the C5-position is blocked. Therefore, this method provides a one pot access to a wide variety of isothiazolinone derivatives allowing to modify easily their biological properties.