期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 19, 期 52, 页码 17926-17938出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201303384
关键词
1; 3-diketones; carbonylation; palladium; reaction mechanisms; synthetic methods
资金
- National Research Foundation [DNRF59]
- Villum Foundation
- Danish Council for Independent Research: Technology and Production Sciences
- Lundbeck Foundation
- Carlsberg Foundation
- Aarhus University
Reaction conditions for the three-component synthesis of aryl 1,3-diketones are reported applying the palladium-catalyzed carbonylative -arylation of ketones with aryl bromides. The optimal conditions were found by using a catalytic system derived from [Pd(dba)(2)] (dba=dibenzylideneacetone) as the palladium source and 1,3-bis(diphenylphosphino)propane (DPPP) as the bidentate ligand. These transformations were run in the two-chamber reactor, COware, applying only 1.5equivalents of carbon monoxide generated from the CO-releasing compound, 9-methylfluorene-9-carbonyl chloride (COgen). The methodology proved adaptable to a wide variety of aryl and heteroaryl bromides leading to a diverse range of aryl 1,3-diketones. A mechanistic investigation of this transformation relying on P-31 and (CNMR)-C-13 spectroscopy was undertaken to determine the possible catalytic pathway. Our results revealed that the combination of [Pd(dba)(2)] and DPPP was only reactive towards 4-bromoanisole in the presence of the sodium enolate of propiophenone suggesting that a [Pd(dppp)(enolate)] anion was initially generated before the oxidative-addition step. Subsequent CO insertion into an [Pd(Ar)(dppp)(enolate)] species provided the 1,3-diketone. These results indicate that a catalytic cycle, different from the classical carbonylation mechanism proposed by Heck, is operating. To investigate the effect of the dba ligand, the Pd-0 precursor, [Pd((3)-1-PhC3H4)((5)-C5H5)], was examined. In the presence of DPPP, and in contrast to [Pd(dba)(2)], its oxidative addition with 4-bromoanisole occurred smoothly providing the [PdBr(Ar)(dppp)] complex. After treatment with CO, the acyl complex [Pd(CO)Br(Ar)(dppp)] was generated, however, its treatment with the sodium enolate led exclusively to the acylated enol in high yield. Nevertheless, the carbonylative -arylation of 4-bromoanisole with either catalytic or stoichiometric [Pd((3)-1-PhC3H4)((5)-C5H5)] over a short reaction time, led to the 1,3-diketone product. Because none of the acylated enol was detected, this implied that a similar mechanistic pathway is operating as that observed for the same transformation with [Pd(dba)(2)] as the Pd source.
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