Abstract
An efficient and stereoselective catalytic system for the Heck cross coupling reaction using novel 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (1, LHX) and Pd(OAc)2 loading has been reported. The palladium complexes derived from the salts 1a-f prepared in situ exhibit good catalytic activity in the Heck coupling reaction of aryl bromides under mild conditions.
Highlights
The Heck reaction, one of the most utilized cross-coupling reactions, is the palladium-catalyzed arylation of an olefin with an aryl halide under basic conditions
The use of immobilized [16] and non-immobilized [17] ligand free palladium salts for the Mizoroki–Heck reaction with chloro- and bromoarenes is discussed in the literature
We have previously reported the use of an in situ formed imidazolidine, tetrahydropyrimidine, tetrahydrodiazepine, benzimidazole-2-ylidene-palladium(II) system which exhibits high activity in various coupling reactions of aryl bromides and aryl chlorides [49,50,51,52]
Summary
The Heck reaction, one of the most utilized cross-coupling reactions, is the palladium-catalyzed arylation of an olefin with an aryl halide under basic conditions. Heck coupling reactions often require high temperatures (normally 110–180 °C) to proceed, even with activated aryl bromides [20,21,22,23,24]. We have previously reported the use of an in situ formed imidazolidine, tetrahydropyrimidine, tetrahydrodiazepine, benzimidazole-2-ylidene-palladium(II) system which exhibits high activity in various coupling reactions of aryl bromides and aryl chlorides [49,50,51,52]. In order to find more efficient palladium catalysts we have prepared a series of new 1,3-dialkyl-3,4,5,6- tetrahydropyrimidinium 1a-f (Scheme 1), and we report the use of the in situ generated catalytic system composed of Pd(OAc) as palladium source, 1a-f as carbene precursors and K2CO3 as a base for cross coupling of aryl bromides with phenylstyrene in DMF/water at 80 °C for 4 h
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