Dibenzylideneacetone with palladium ligand

The catalyst reported by Drent [48] was generated in situ by mixing a palladium source with the ligand. A palladium source is broadly defined as a complex or any form of palladium metal whereby upon mixing with the ligand an active catalyst is formed. Many palladium sources are possible, but the sources exemplified by Drent aretris(dibenzylideneacetone)dipalladium(0)(Pd2(dba)3),bis(dibenzylideneacetone) palladium(O) (Pd(dba)2), or palladium(II) acetate. 

Buchwald has shown that, in combination with palladium(II) acetate or Pd2(dba)3 [tris(dibenzylideneacetone)dipalladium], the Merrifield resin-bound electron-rich dialkylphosphinobiphenyl ligand (45) (Scheme 4.29) forms the active polymer-supported catalysts for amination and Suzuki reactions [121]. Inactivated aryl iodides, bromides, or even chlorides can be employed as substrates in these reactions. The catalyst derived from ligand (45) and a palladium source can be recycled for both amination and Suzuki reactions without addition of palladium. 

An inventive synthesis of (—)-swainsonine (378) by Trost and Patterson took advantage of the enantioselective desymmetrization of the mese-bis (carbamate) 514 with tris(dibenzylideneacetone)bis(palladium) in the presence of the chiral bis (phosphine) ligand (i .,J )-515 in order to achieve the... 

Cyclocarbonylation of o-iodophenols 503 with isocyanates or carbodiimides and carbon monoxide in the presence of a catalytic amount of a palladium catalyst (tris(dibenzylideneacetone)dipalladium(O) Pd2(DBA)3) and l,4-bis(di-phenylphosphino)butane (dppb) resulted in formation of l,3-benzoxazine-2,4-diones 504 or 2-imino-l,3-benzoxazin-4-ones 505 (Scheme 94). The product yields were dependent on the nature of the substrate, the catalyst, the solvent, the base, and the phosphine ligand. The reactions of o-iodophenols with unsymmetrical carbodiimides bearing an alkyl and an aryl substituent afforded 2-alkylimino-3-aryl-l,3-benzoxazin-4-ones 505 in a completely regioselective manner <1999JOC9194>. On the palladium-catalyzed cyclocarbonylation of o-iodoanilines with acyl chlorides and carbon monoxide, 2-substituted-4f/-3,l-benzoxazin-4-ones were obtained <19990L1619>. 

Acylation of aryl and alkenyl halides. The zinc salts of enol ethers and allenic ethers couple with aryl and alkenyl halides in the presence of several Pd(0) catalysts Pd[P(QH,),l4 or bis(dibenzylideneacetone)palladium with added phosphine ligands. 

The success of cycloisomerization reactions of this type is critically dependent on factors that influence the conformational mobility of the side chain bearing the alkene moiety. Additionally, functional groups which are able to serve as ligands at palladium may also be of importance. As an example, neither the (E)- nor the (Z)-crotonate derivative ( -IS or (Z)-13 gives rise to the formation of bicyclic products on treatment with bis(dibenzylideneacetone)palladium/tri-isopropyl phosphite. Instead, the corresponding isomeric substituted butadienes, methyl (2E or 2Z,6 )-7,8-dimethylnona-2,6,8-trienoate (14) and methyl (2E or 2Z)-8-methyl-7-methyl-enenona-2,8-dienoate (15), are formed. 

Finally, more complex ligands will generally add extra cost. This can be illustrated in the field of palladium-catalysed coupling chemistry.13 Within the literature two palladium-precursors dominate Pd(OAc)2 and Pd(dba)2 (or Pd2(dba)3) (dba = dibenzylideneacetone). These are often interchangeable, with no simple pattern to which is more efficient. However, in an industrial setting, the cost of the ligands will affect the overall cost of the catalyst pre-cursor. The acetate ligand is derived from acetic acid, which is substantially cheaper than dba. 

The first time that a Mizoroki-Heck reaction was conducted in a flnorons system was in 1999 when Sinou and coworkers [71] applied Pd2(dba)3 (dba = dibenzylideneacetone) or Pd(OAc)2 and a perflnorinaled phosphine (e.g. 28-30) in a perflnorinated-nonflnorons solvent mixture in the Mizoroki-Heck reaction of aryl iodides (4h, 80 °C). In this system, the Mizoroki-Heck prodnct was soluble in acetonitrile and the catalyst was dissolved in the fluorous phase. However, some ligand was lost due to its partial solubility in acetonitrile and some of the palladinm was reduced to palladium black. Thus, after each run with the recovered catalyst, lower conversions were obtained. 

Norbomene has also been utilized in a one-step construction of C2-symmetrical pallada(IV)spirocycle complexes featuring one palladium(IV)-Csp bond and one palladium(IV)-0 bond in each palladacyclic ring (Scheme 14) [24]. Oxidative cyclization of norbomene or benzonorbomadiene with chloranil and Pd2(dba)3 (dba = dibenzylideneacetone) afforded new palladium(IV) complexes bearing various Lewis basic ligands (L = pyridine, THF, and diethyl ether). Selected complexes were characterized by X-ray crystallography. Notably, these palladium (IV) complexes proved to be stable for prolonged periods of time at room temperature, both in the solid state and in solution. The complexes decomposed upon... 

Heck reactions are often carried out using palladium(O) complexes. Tetrakis(triphenylphosphine)palladium(0) is frequently used, but does not allow the chemist to vary either the identity of the ligand, or the lig-andipalladium ratio. A more convenient mixture is to use the air-stable palladium(O) dibenzylideneacetone complex with the added ligands of choice. It is, however, not necessary to use a palladium(O) pre-catalyst. Palladium(II) salts, especially the more soluble palladium(II) acetate, are often used, with added phosphines. The palladium(II) salts are reduced to palladium(O) in situ. 

Palladium(0) complexes with the weak ligand dibenzylideneacetone (Figure 5-4) not only are commercially available but also serve as valuable precatalysts for a number of reactions (e.g.. Scheme 5-38). Depending on the synthesis procedures, Pd(dba)2, Pd2(dba)3 CHCl3 and/or other stoichiometries can be obtained. Recrystallization provided the pure complexes. In some cross-coupling reactions, the commercially available modified dibenzylideneacetone ligand 3,5,3, 5 -... 

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