Palladium complexes substitution

In a continuation of their work, they also reported the cross-eoupling reactions between MBH acetates and bimetallic reagents (Si-Si, Ge-Ge) catalyzed by a phosphine-free palladium complex. Substituted-2-carbonylallylsi-lanes 375 and allylgermanes 376 were isolated in high yields with regio- and stereoselectivity (Scheme 3.167). ... 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

Helquist et al. [129] have reported molecular mechanics calculations to predict the suitability of a number of chiral-substituted phenanthrolines and their corresponding palladium-complexes for use in asymmetric nucleophilic substitutions of allylic acetates. Good correlation was obtained with experimental results, the highest levels of asymmetric induction being predicted and obtained with a readily available 2-(2-bornyl)-phenanthroline ligand (90 in Scheme 50). Kocovsky et al. [130] prepared a series of chiral bipyridines, also derived from monoterpene (namely pinocarvone or myrtenal). They synthesized and characterized corresponding Mo complexes, which were found to be moderately enantioselective in allylic substitution (up to 22%). 

In the case of 3-alkynylamines, IH proceeds exclusively in a S-Endo-Dig process to give substituted 1-pyrrolines. The best catalysts are palladium complexes (Eq. 4.69) the reaction fails for terminal alkyne owing to the formation of a stable palladium acetylide [278]. 

At the beginning of the 1970s a convenient procedure was described for converting olefins into substituted butanedioates, namely through a Pd(II)-cata-lysed bisalkoxycarbonylation reaction. So far various catalytic systems have been applied to this process, but it took twenty years before the first examples of an enantioselective bisalkoxycarbonylation of olefins were reported. Ever since, the asymmetric bisalkoxycarbonylation of alkenes catalysed by palladium complexes bearing chiral ligands has attracted much attention. The products of these reactions are important intermediates in the syntheses of pharmaceuticals such as 2-arylpropionic acids, the most important class of... 

Nucleophilic Substitution of xi-Allyl Palladium Complexes. TT-Allyl palladium species are subject to a number of useful reactions that result in allylation of nucleophiles.114 The reaction can be applied to carbon-carbon bond formation using relatively stable carbanions, such as those derived from malonate esters and (3-sulfonyl esters.115 The TT-allyl complexes are usually generated in situ by reaction of an allylic acetate with a catalytic amount of fefrafcz s-(triphenylphosphine)palladium... 

The mechanism for the reaction catalyzed by cationic palladium complexes (Scheme 24) differs from that proposed for early transition metal complexes, as well as from that suggested for the reaction shown in Eq. 17. For this catalyst system, the alkene substrate inserts into a Pd - Si bond a rather than a Pd-H bond [63]. Hydrosilylation of methylpalladium complex 100 then provides methane and palladium silyl species 112 (Scheme 24). Complex 112 coordinates to and inserts into the least substituted olefin regioselectively and irreversibly to provide 113 after coordination of the second alkene. Insertion into the second alkene through a boat-like transition state leads to trans cyclopentane 114, and o-bond metathesis (or oxidative addition/reductive elimination) leads to the observed trans stereochemistry of product 101a with regeneration of 112 [69]. 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

It has been found that A-tosyl aziridines undergo oxidative addition to palladium complexes to form azapalladacyclobutanes <06JA15415>. Reaction of aziridine 95 with Pd2(dba)3 and 1,10-phenanthroline provides the palladacycle 96 in 45% isolated yield. This compound is an air stable solid. Treatment the palladacycle 96 with catalytic Cul is believed to open the palladacycle to form a copper intermediate, which cyclizes to cyclopentyl alkylpalladium intermediate 97. Loss of Cul then provides the product palladacycle 97 as an air stable solid. Several different aziridines were examined in this reaction. Only a limited set of olefin substituted aziridines provided the azapalladacyclobutanes (e.g. 96). 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

The mercuration of phosphonium derivatives has also been observed. The methylene group of the dimeric palladium complex 63 substituted by a carbonyl and a phosphonium functionality is readily mercurated upon reaction with Hg(OAc)2 to afford complex 64 (Equation (22)).7 Further studies demonstrated that the presence of a triphenylphosphonium group alone is sufficient to promote proton-mercury exchange. For example, the reaction of... 

These studies were extended to hydrosilation of cyclopentadiene with trichlorosilane (52). This is most difficult with platinum catalysts. Palladium complexes favored production of 1 1 adducts as a mixture of 3- and 4-trichlorosilylcyclopentene. Nickel complexes produced substantial amounts of 1 2 adducts as trichlorosilyl-substituted 4,7-methylene-4,7,-8,9-tetrahydroindanes, with the exception of nickel tetracarbonyl, which was very active and selectively formed almost exclusively 3-trichlorosi-lylcyclopentene with no 1 2 adduct. 

Some synthetically useful isomerization reactions of alkenes, other than nitrogen- or oxygen-substituted allylic compounds, were reported by the use of a catalytic amount of transition metal complexes. The palladium complex, /ra r-Pd(C6HsCN)2Gl2, effectively catalyzed the stereoselective isomerization of /3,7-unsaturated esters to a,/3-unsaturated esters (Equation (26)). 

Murakami and co-workers have shown that phenyl- and vinyl-substituted vinylallenes react in a palladium-catalyzed intermolecular [4+ 4]-cycloaddition in the presence of a palladium complex to give the cyclooctadiene cycloadducts in moderate to good yields (Scheme 29).103 In a method reported by Lee and Lee, bicyclo[6.4.0]-dodecatrienes are prepared in good overall yields via a two-step, one-flask procedure that involves a serial palladium-catalyzed cross-coupling/[4 + 4]-cycloaddition followed by [4 + 2]-cycloaddition (Scheme 30). Overall, this two-step process impressively brings together five simple components to form relatively complex bicyclic products.1... 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

Substituting the benzene ring with a double bond, Pd-catalyzed intramolecular alkoxylation of alkyne 122 also proceeded via an alkenyl palladium complex to form furan 123 instead of a benzofurans [99, 100]. In addition, 3-hydroxyalkylbenzo[fc]furans was prepared by Bishop et al via a Pd-catalyzed heteroannulation of silyl-protected alkynols with 2-iodophenol in a fashion akin to the Larock indole synthesis, [101]. 

Thiazole is a jt-electron-excessive heterocycle. The electronegativity of the N-atom at the 3-position makes C(2) partially electropositive and therefore susceptible to nucleophilic attack. In contrast, electrophilic substitution of thiazoles preferentially takes place at the electron-rich C(5) position. More relevant to palladium chemistry, 2-halothiazoles and 2-halobenzothiazoles are prone to undergo oxidative addition to Pd(0) and the resulting o-heteroaryl palladium complexes participate in various coupling reactions. Even 2-chlorothiazole and 2-chlorobenzothiazole are viable substrates for Pd-catalyzed reactions. 

Lehn has also reported the hydrogen-bonding templated assembly of receptors based on bipyridine copper and palladium complexes [102]. A mixture of substituted bipyridines (76, 77) (see Scheme 39) with copper(I) triflate generates a mixture of tetrahedral complexes and uncoordinated ligands. 

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