Catalytic Chlorination And Acylation Of 2-Arylpyridines And Facile Construction Of Benzoxazole Ring

The palladium-catalyzed ortho-chlorination and acylation of 2-arylpyridines with arylmethyl chlorides as the chlorination or acylation reagents were developed; a protocol for the facile synthesis of 2-arylbenzoxazoles via copper-catalyzed o-aminophenol derivatives using arylmethyl chlorides as the new acyl sources was established.1 The ortho-chlorination or acylation of 2-arylpyridines with arylmethyl chlorides as the cheap chlorine or acyl source was performed in the presence of TBHP as the oxidant employing palladium chloride or cyclopalladated ferrocenylimine as the catalyst, respectively, affording the chlorinated and acylated products in mostly moderate to good yields (Scheme 1). This transformation exhibited high regioselectivity for the substrates bearing a meta-substituent in the benzene ring, and almost occurred at the less sterically hindered ortho-C-H bond of the directing group. All the new compounds were characterized by 1H NMR,13C NMR and HRMS.2 A new route to 2-arylbenzoxazoles via copper-catalyzed tandem condensation/oxidative reaction of o-aminophenol derivatives with arylmethyl chlorides was developed. Note that this reaction utilized arylmethyl chlorides as a new type of cheap acyl sources and KNO3 as a readily available and low-cost benign oxidant, affording the desired products in mostly moderate to good yields in chlorobenzene (Scheme 2). This transformation can tolerate variousfunctional groups well and also be applied to the synthesis of benzimidazoles and benzothiazoles. All the new compounds were characterized by 1H NMR,13C NMR and HRMS.