Palladium acetate silver salts

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

The iodo acetal could be easily obtained (as a mixture of E and Z isomers, 40/60), by a nickel catalyzed iodine-bromine exchange. This synthon reacted smoothly with the C15 tertiary allylic alcohol in the presence of a catalytic amount of palladium acetate and a stoechiometric amount of either a silver or a thallium salt. The C20 hydroxy-acetal was obtained in 38% yield, as a mixture of E and Z isomers (48/52). Finally retinal was obtained by treatment with dilute HBr in refluxing acetone, as a mixture of E and Z isomers (C(9)=C(io) and C(i3)=C(i4)), Fig. (32). 

The fact that the decomposition of ozonides is catalyzed by finely divided metals (silver, platinum, palladium) and metal salts such as ferrous sulfate suggests a free-radical mechanism.23 2-Butene ozonide is broken down with dilute ferrous sulfate solution into acetic acid and acetaldehyde.23... 

Shi has reported a method for /V-alkylanilidc arylation by simple arenes [53], The reaction conditions include heating the anilide with excess arene in propionic acid in the presence of catalytic palladium acetate and copper triflate under oxygen atmosphere. Use of monosubstituted arenes leads to the formation of isomer mixtures however, from the point of atom economy C-H/C-H couplings are the most efficient way for formation of C-C bonds if oxygen is used as the terminal oxidant. Shi has also reported that anilides can be coupled with arylboronic acids and trialkoxyaryl-silanes [54, 55], Silver and copper salts are used as terminal oxidants. 

The cascade process was initially explored with prochiral trienyl iodide 44 (Scheme 16.11) [36, 37]. Mizoroki-Heck cyclization of this precursor produced -ally(palladium species 45, which was trapped by acetate at the least-hindered terminus of the ry -aWyl system to provide CM-bicyclo[3.3.0]octadiene 46 in 60% yield, albeit with very low enantioselectivity (20% ee). Attempts to use silver salts as halide scavengers in this reaction led to the decomposition of 44, presumably resulting from the sensitivity of the cyclopentadienyl moiety. Mizoroki-Heck cyclization of prochiral vinyl triflate 47 with Pd(OAc)2, (S)-BINAP and tetrabutylammonium acetate was more productive, giving diquinane product 48 in excellent yield and 80% ee (Scheme 16.12). The corresponding allylic amine 49 was obtained in analogous fashion using benzylamine as the nucleophile [38]. Allylic acetate 48 was elaborated in seven steps to triquinane /3-ketoester 50, an intermediate in Shibasaki and coworkers [39] earlier total syntheses of ( )-A -capnellene-3/3,8/3,10a-triol (51) and )-A. -c3i me ene-5p, P,l0a,lA-i xdiO (52). 

The effect of silver salts, copper acetate and mercury acetate as an additive was studied in the palladium-catalyzed carbonylation of nitrobenzene [17]. The combination of palladium acetate, sliver fluoride, 1,10-phenanthroline and p-toluen-sulfonic acid were found to be highly active and selective yielding nitrobenzene conversion up to 96 %. Copper acetate and mercury acetate are also effective as additives and gave good results. A-phenylcarbamate was produced in the presence of alcohol. 

When hydrochloric acid solutions of noble metal salts are being tested, the presence of silver salts need not be considered. Gold chloride can be removed by shaking the strong hydrochloric acid solution with ether or ethyl acetate. The gold-free aqueous solution should be taken to dryness to remove the excess hydrochloric acid before the test with / -nitroso-diphenylamine is tried. There is as yet no method for the removal of platinum which is suitable for the spot test technique. Since the identification limit of the platinum reaction with />-nitrosodiphenylamine is 10 y, the palladium test just given is not impaired by small amounts of platinum. 

The coupling of anilines with arylboronic acids has been described in a process catalysed by palladium acetate without the need for ligands, bases, or salts. The mechanism shown in Scheme 17, where S represents solvent, involves in situ formation of the dia-zonium salt from the aniline, and formation of an arylpalladium alkoxo complex which allows the transmetallation step with arylboronic acids. It has been shown that a free amine may be used as a DG in a palladium-catalysed reaction promoted by soluble silver salts. The latter aid the formation of intermediates, (136), which may undergo cyclopalladation followed by transmetallation with an arylboronic acid and reductive elimination. Related work has shown thatbiaryl-2-amines may react with aryl iodides in the presence of palladium acetate and silver acetate to give mono- or di-arylated species such as (137). 

Commercially available trimethylvinylsilanes can be vinylated using either vinyl triflates or vinyl iodides in the presence of silver salts, in a reaction catalyzed hy palladium acetate in the presence of triethylamine. The resulting 3-substituted 1-trimethylsilyl-1,3-dienes are obtained in reasonable to good yields. ... 

The transformation from arenes into phenol acetates can be achieved with hypervalent iodine compounds (such as phenyliodonium acetate, PhI(OAc)2), with chromates, or under aerobic conditions. Ligands, like picolinic acids, stabilize the intermediate palladium(IV) salts. In the presence of Lewis acids or silver salts, biaryl formation takes place. The influence of different directing groups has recently been reviewed. For example, diaryl sulfones or sulfoxides having at least one heteroaryl attached can be oxidized to the corresponding aryl acetates (Scheme 5-194, Experimental Procedure below). ... 

Silver acetate has a small catalytic effect on the alkene substitution reaction but 5 equiv. of the salt only give 140% of stilbene in the styrene phenylation, based upon palladium.15 The same reaction carried out at 80 C under 300 lbf in-2 (1 lbf in-2 = 6.89 kPa) of oxygen gives stilbene in 248% yield, based upon palladium.16 The best reoxidation reagent is f-butyl perbenzoate, which yields 10-14 turnovers of the palladium in the vinyl substitution of cinnamaldehyde and similar alkenes with benzene.17... 

Palladium salts can be utilized catalytically in the presence of silver or copper acetate and oxygen.578,586 587 This reaction offers an attractive route for the direct vinylation of benzene to styrene586 587 ... 

The obtained amino functionalised imidazolium salts could be used to generate the corresponding palladium(ll) carbene complexes using the silver(l) complexes as carbene transfer agents. Application of these palladium(ll) complexes (predominantly in situ) in asymmetric allylic alkylation reactions between ( )-l,3-diphenylprop-3-enyl acetate and dimethyl malonate (a standard reaction for this catalytic process [145]) gave up to 80% ee,... 

Yang et al. used a similar protocol (an ether functionality supported on a primary alkyl halide carrier) to introduce an acetal on either side of the imidazole ring generating an ether functionalised ionic liquid (IL) imidazolium salt [183] (see Rguie 3.58). The anion could be varied without loss of the IL property (melting point below 1(X) °C) [184]. Synthesis of the transition metal carbene complexes (palladium) was done by carbene transfer ftom the corresponding silver(I) complexes or by reaction with the metal acetate (nickel) [162] (see Figure 3.64). 

A few years earlier, Herrmann et al. published a carboxylic ester functionalised imi-dazolium salt that was synthesised directly from imidazole and bromoacetic acid ethyl ester [216]. Owing to its method of synthesis the imidazolium salt is C -symmetric with two ester functional wingUp groups. Generation of the rhodium(I) and palladium(II) carbene complexes was realised by reaction of the imidazolium salt with a rhodium alkoxide precursor or with palladium(II) acetate in the presence of NaOEt and Nal (see Figure 3.76). The silver(I) oxide method had not been discussed in the literature at the time [11]. 

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