Palladium Catalyzed Suzuki And Heck Reactions And Synthesis Of Pyrrole Derivatives

The palladium-catalyzed coupling reaction is one of the most important methodsfor synthesis of C-C bond. These coupling products were found widely applications asintermediates in the preparation of pharmaceuticals, materials, natural products, aswell as industry. Classical palladium-catalysed reactions such as Suzuki-Miyaura andMizoroki-Heck couplings attract much attention due to its high efficiency and widetoleration to substrates. We described the synthesis of a new type ofnitrogen-containing dendrimers capped with DABCO groups up to the thirdgeneration and the use of the corresponding palladium particles immobilized on it ascatalysts for Suzuki-Miyaura, Mizoroki-Heck coupling reactions.The direct coupling of heteroarenes with aryl halides via a C–H bondactivation/functionalisation provides a cost-effective and environmentally attractiveprocedure for the preparation of arylated heteroarenes. Such couplings are veryattractive compared to classical palladium-catalysed reactions as they do not requirethe preliminary synthesis of organometallic derivatives. We report herein the firstregioselective palladium-catalysed direct C5-arylations of C3-substituted pyrrolederivatives with aryl halides. This method should give access to several syntheticallyimportant pyrroles derivatives. The details are as follows:1. A new kind of silica supported third generation dendrimers capped by1,4-diaza-bicyclo[2.2.2]octane (DABCO) groups stabilized palladium (0) nanoparticlesand their enhanced catalytic activity in Suzuki-Miyaura, and Mizoroki-Heck reactionsin excellent yields under mild conditions. The advantages of this procedure are simpleoperation, short reaction time, trace amount of catalyst, good to excellent yields,environmental friendly. Furthermore, it can be easily recovered and reused.2. The PdCl(C3H5)(dppb)/KOAc system was found to be effective for the directregioselective C5-arylation of3-acetylpyrroles with ortho-substituted aryl bromides.31new coupling products which have potential for medicinal chemistry were synthesizedsuccessfully.