PaUadium complexes synthesis

Uozumi, Y. Suzuka, T. pi-AUyhc sulfonylation in water with amphiphilic resin-supported paUadium-phosphine complexes. Synthesis 2008,1960-1964. 

Coupling of n- allylic)paUadium complexes with an alkenylzirconium(IV) complex l,4-< enes.2 A recent stereospecific synthesis of natural (20R)-cholestanone-3 (4) involves coupling of the alkenylzirconium complex 2 with the jr-(allylic)palladium chloride dimer (1) of a (Z)-17(2U)-pregnene. The major product is a 1,4-diene (3), formed by regioselective attack of 2 at C20, the less hindered terminus of the allylic unit, and with inversion at C20. Coupling of 2 with the 7i-(allylic)palladium chloride dimer of the (E)-isomer of 1 results in a 1,4-diene epimeric at C20 with 3. Hydrogenation of the diene completes the synthesis of the desired natural cholestanone-3 (4). 

In acyclic systems the 1,4-relative stereoselectivity was controlled by the stereochemistry of the diene. Thus, oxidation of (E,E)- and ( ,Z)-2,4-hexadienes to their corresponding diacetates affords dl (>88% dl) and meso (>95% meso) 2,5-diacetoxy-3-hexene, respectively. A mechanism involving a trani-acetoxypalladation of the conjugated diene to give an intermediate ( 7r-allyl)paUadium complex, followed by either a cis or tram attack by acetate on the allyl group, has been suggested. The cis attack is explained by a cis migration from a (cr-allyl)palladium intermediate. The diacetoxylation reaction was applied to the preparation of a key intermediate for the synthesis of d/-shikimic acid, 3,... 

Polystyrene is the most frequently used polymeric support for the immobiUzation of paUadium complexes [15]. The PS resins are weU developed in the field of soUd-phase peptide synthesis. Therefore resins bearing various chemical functional groups, diameter size, loading value, degree of cross-linking, for example, are now commerciaUy readily avaUable to permit investigation of these variables on the catalytic property. The most widely used polystyrene in... 

Pytkowicz, J., Roland, S., Mangeney, P. et al. (2003) Chiral diaminocarbene paUadium(II) complexes synthesis, reduction to Pd(0) and activity in the Mizoroki-Heck reaction as recyclable catalysts. J. Organomet. Chem., 678, 166-79. 

The antifungal, antiviral agent (+)-brefeldin A, whose recent synthesis using rr-allyl-paUadium complexes has previously been described (Scheme 24), was prepared by Trost et using the [3 + 2] cycloaddition to form the cyclopentyl ring (Scheme 41). Chiral acrylate 190, prepared from mannitol, was subjected to cyclizalion conditions to give cycloadduct 191 in 87% yield and an excellent selectivity. Diastereoselectivity in the cycloaddition extended the stereochemistry of 190 into the absolute stereochemistry of 191, generating three of the live stereocenters of brefeldin A. After ozonolysis, reduction, and protection, the lower side chain was attached to prepare the sulfone 192. The upper side chain was then introduced, and further functionalization led to the key intermediate 194, which had already been transformed to (+)-brefeldin A. 

N. Batail, A. Bendjeriou, L. Djakovitch, V. EHtfaud, Larock indole synthesis using paUadium complexes immobilized onto mesoporous siUca, Appl. Catal. A Gen. 388 (2010) 179-187. 

McCall AS, Wang H, Desper JM, Kraft S. Bis-N-heterocyclic carbene paUadium(IV) tetrachloride complexes synthesis, reactivity, and mechanisms of direct chlorinations and oxidations of organic substrates. J Chem Soc. 2011 133 1832-1848. 

The two carbene units can be embedded in a (macro)cyclic ring system known as a cyclophane. A standard procedure for the synthesis of such a system starts with a,a -dibromoxylene and potassium imidazolide [368]. Cychsation can be achieved by reacting the bis-imidazole compound with a second equivalent of a,a -dibromoxylene (see Figure 3.116). The cyclic bis-imidazolium cyclophane can then be reacted with paUadium(II) acetate to form the palladium complex [369,370]. The silver(I) and gold(I) complexes are accessible from the reaction with silver(I) oxide [371] and the usual carbene transfer reaction to gold(I) [372]. 

Atypical synthesis of naAed NHC-containing complexes has been reported by Cloke and coworkers. As shown in equation (7), the co-condensation of nickel, paUadium, and platinum vapor with the free NHC, TBu, provided two-coordinated homoleptic complexes of Ni(0), Pd(0), and Pt(0) (43). Unfortunately, in addition to the poor yield of the isolated product, this original methodology required a metal vapor synthesis apparatus. 

Addition of the silicon-boron bond aCTOss carbon-carbon triple bonds (i.e., silabora-tion) is most effectively catalyzed by a paUadium(0)-t rt-alkyl isocyanide complex to give (Z)-l-boryl-2-silyl alkenes with high regio- and stereoselectivity, which are useful for synthesis of stereodefined alkenylsilanes. 

The pseudoisourea paUadium(ll) complex described by Mandapati and coworkers (Scheme 5) has been used by the same group in a solid-phase version. (2013JOM162, 2014JOM31). The polystyrene-supported pseudoisourea paUadium(II) complex was used for 2,3-disubstituted indole synthesis by reaction between the iodoanihne and diphenylacetylene. Among the studied bases and solvents, K2CO3 and DMF gave the best results. 

The oxidation of higher olefins has also been studied, and these reactions form ketones (Equation 16.102). Thus, the C-0 bond formation between water and the substituted olefin mediated by palladium occurs at flie internal carbon. For example, paUadium-catalyzed oxidation of propene forms acetone, and this reaction provides one industrial route to this material. Oxidations of substituted olefins to form ketones have also become a common method for the conversion of olefins to ketones during complex-molecule synthesis. Examples of the use of palladium-catalyzed oxidation in complex-molecule synthesis are described later in this chapter. 

The insertion of CO into Pd-carbon bonds has also been employed in several tandem/cascade reactions that afford five-membered nitrogen heterocycles [97]. A representative example of this approach to the construction of heterocydes involves synthesis of isoindolinones via the Pd-catalyzed coupling of 2-bromobenzaldehyde with two equivalents of a primary amine under an atmosphere of CO [97bj. As shown below (Eq. (1.57)), this method was used for the preparation of 144 in 64% yield. The mechanism of this reaction is likely via initial, reversible condensation of 2-bromobenzaldehyde with 2 equiv of the amine to form an aminal 145. Oxidative addition of the aryl bromide to Pd° followed by CO insertion provides the acylpalladium spedes 146, which is then captured by the pendant aminal to afford the observed product. An alternative mechanism involving intramolecular imine insertion into the Pd—C bond of a related acylpalladium species, followed by formation of a paUadium-amido complex and C—N bond-forming reductive elimination has also been proposed [97b],... 

Nan, G., B. Rao, and M. Luo. 2011. Cw-chelated paUadium(II) complexes of biphenyl-linked bis(imidazolin-2-ylidene) Synthesis and catalytic activity in the Suzuki-Miyaura reaction. Arkivoc 2 29-40. 

Ishiyama, T. Ishida, K. Miyaura, N. 2001. Synthesis of pinacol arylboronates via cross-coupling reaction of bis(pinacolato)diboron with chloroarenes catalyzed by paUadium(0)-tricyclohexylphosphine complexes. Tetrahedron 51 9813-9816. 

Borkar, S., Yennawar, H., and Sen, A. (2007) Methacrylate Insertion into cationic diimine paUadium(II)-alkyl complexes and the synthesis of poly(alkene-Wock-atkene/carbon monoxide) copolymers. Organometallics, 26,4711 714. 

Bonnet LG, Douthwaite RE, Hodgson R. Synthesis of constrained-geometry chiral di-N-heterocyclic carbene ligands and their silver(I) and paUadium(II) complexes. 

Araki S, Wanibe F, Uno F, et al. Synthesis and chemical transformations of 1,3-diaryltetrazolium salts, preparation of mercury(II) and paUadium(II) complexes of... 

Bennett MA, Bhargava SK, Bond AM, Burgar IM, Quo SX, Kar G, Priver SH, Wagler J, Willis AC, Torriero AAJ (2010) Synthesis, X-ray structure and electrochemical oxidation of paUadium(II) complexes of ferrocenyldiphenylphosphine. Dalton Trans 39(38) 9079-9090... 

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