Palladium acetate catalysis

Several reports have been made of a successful catalyzed addition/ substitution reaction resulting in direct attachment of phosphorus to aromatic rings. The preparation of mixed triarylphosphines has been accomplished by the reaction of tin- or silicon-substituted diphe-nylphosphines with aryl halides catalyzed by palladium reagents.74 A similar transformation has also been reported using nickel catalysis.75 The addition/substitution of diphenylphosphine to triflate functionalized phenolic linkages has been of use for the preparation of substances as analogues of tyrosine-related amino acid derivatives, accomplished with catalysis by palladium acetate (Equation 4.29).76... 

If allenes bear a potential leaving group in the a-position to the cumulene system, they are very attractive substrates for palladium-catalyzed substitutions. Examples are a-allenic acetates and particularly a-allenic phosphates, which react under palladium(O) catalysis with carbanions derived from /3-diesters, /i-keto esters, a-phenylsulfonyl esters and glycine ester derivatives. They lead to /3-functionalized allenes such as 86, 89 and 93 (Eqs. 14.9-14.11) [45 18]. 

The intramolecular palladium catalyzed ring closure of the tetrahydro-isoquinoline derivative depicted in 8.41. led to the formation of the aporphine derivative in good yield, which was then converted into racemic aporphine in three steps. In the ring closing step 20 mol% palladium acetate and 40 mol% tricyclohexylphosphine were used as catalyst. The removal of the hydroxyl group was also achieved by palladium catalysis through its conversion to triflate and the subsequent reduction with ammonium formate in the presence of palladium acetate and dppf.53... 

In this way, the consecutive reactions to give higher amines in the aqueous phase are avoided in contrast, these reactions are unavoidable in the homogeneous one-phase catalysis. The catalyst system consists of palladium acetate/tppts dissolved in water the second phase is an organic solvent such as toluene. 

In contrast, the closely related palladium acetate-promoted intramolecular alkylation of alkenes by tri-methylsilyl enol ethers (Scheme 4)6,7 has been used to synthesize a large number of bridged carbocyclic systems (Table 1). In principle, this process should be capable of being made catalytic in palladium(II), since silyl enol ethers are stable to a range of oxidants used to carry the Pd° -> Pd11 redox chemistry required for catalysis. In practice, catalytically efficient conditions have not yet been developed, and the reaction is usually carried out using a full equivalent of palladium(II) acetate. This chemistry has been used in the synthesis of quadrone (equation 2).8 With the more electrophilic palladium(II) trifluoroace-tate, methyl enol ethers underwent this cyclization process (equation 3).9... 

The present procedure uses palladium catalysis in the first step and in one of the second steps. These reactions occur under very mild conditions (room temperature) and the catalyst used is commercial palladium acetate. 

The synthesis of ethyl 3,3-diethoxypropanoate, 5, described here implies acylation of an enol ether followed by a haloform reaction. The procedure is superior to other methods, which afford mixtures of acetals and acrylates,4 give only moderate yields,5 6 7 require the troublesome use of ketene8 or expensive ethyl propiolate,9 10 11 need palladium(ll) catalysis,12 or equipment for electrochemical reactions.13... 

The synthesis of five-membered carbo- and hetero-cyclic compounds, including fused rings, has been reported using acetate as a nucleophile in the cyclization of 1,6-enynes under palladium(II) catalysis (Scheme 91). The reaction is initiated by trans-acetoxypalladation of the alkynes and quenched by either trans- or ra-deaceloxypal-ladation in the presence of 2,2/-bipyridine as the ligand.134... 

Palladium(II) catalysis (0.01-0.04 equiv) is more effective and leads to higher selectivity than mercury(II) catalysis912. With bis(acetonitrile)palladium(II) chloride [Pd(CH3CN)2CI2] as catalyst the efficiency decreases in the order carbamates > allylic acetates > carbonates. 

In another study, these workers found that cis complexes of palladium acetate with bidentate ligands such as o-phenanthroline will catalyze the exchange at higher temperatures (190). As trans complexes were inactive, it is likely that two adjacent cis coordination positions are required for catalysis. These new catalysts are extremely interesting and deserve further mechanistic study. 

O/t/20-arylation of benzoic acids is often preferable to ortho-arylation of benzamides if conversion of the amide moiety to other functional groups is desired. However, only a few reports have dealt with the orf/io-functionalization of free benzoic acids due to challenges that involve such transformations. The reactions can be complicated by decarboxylation of the product and the starting material. Despite those difficulties, several methods for direct o/t/io-arylation of benzoic acids have been developed. Yu has shown that arylboronates are effective in arylation of benzoic acids under palladium catalysis [59], The reactions require the presence of palladium acetate catalyst, silver carbonate oxidant, and benzoquinone. Even more interestingly, the procedure is applicable to the arylation of unactivated sp3 C-H bonds in tertiary carboxylic acids such as pivalic acid (Scheme 13) if aryl iodide coupling partner is used. Aryl trifluoroborates can also be used [60],... 

The a,/J-unsaturated acetal 24 reacts with diazomethane under palladium(II) acetate catalysis to provide the oxazolidinyl-substituted cyclopropane 25 with high diastereomeric purity. Subsequent hydrolysis gives (-)-(l,R,2/ )-fraft.v-2-phenylcyclopropanecarboxaldehyde with recovery of the ( —)-2-methylamino-l-phenyl-l-propanol [(-)-ephedrine] auxiliary79. 

Allylic aeetates or carbonates can undergo nucleophilic substitutions via palla-dium(0)-catalysis (11). In this paper, we report on the extension of this reaction to unsaturated fatty aeids by the preparation of allyl carbonates and acetates of oleic, linoleic, and 10-undecenoic acid and their substitution with carbon- and heteroatom-nucleophiles by palladium(0)-catalysis. In this way, different substituents can be in-trodueed into the alkyl chain of fatty acids. This leads to fatty acid derivatives in which the properties of biologically active compounds may possibly be combined with the amphiphilic property of the fatty acid. 

In allylacetates, the acetoxy group can be substituted by way of palladium(O)-catalysis. Abase must be added to generate a nucleophilic anion and to neutralize the acetic acid. Allyl carbonates A (Scheme 1) are better substrates for the substitution by palladium(0)-catalysis than actetates because they require no base and thus tolerate... 

The allyl diacetate [9] can be obtained in 80% yield and in a very simple reaction by electrolysis of methyl konjuenate in an undivided cell in acetic acid as solvent (see above). It was therefore of great interest to determine whether this readily available acetate also reacts with nucleophiles under palladium(0)-catalysis. Indeed, [9] can be joined to carbon nucleophiles in moderate to good yield to form the conjugates [42] and [43] (Eq. 21). A disubstitution could not be enforced, however, despite the use of a fivefold excess of the nucleophile. 

Many examples of alkene and alkyne insertion into metal-carbon bonds can also be found in the section on homogeneous catalysis. Other recent examples include the insertion of conjugated dienes into palladium-allyl bonds, olefin arylation in the presence of palladium acetate, and the reaction of ethylene with arylmagnesium halides in the presence of nickel chloride. Reaction of isocyanates with nickel-ethynyl compounds... 

Acetoxyindole derivatives have been prepared by the reaction of Af-benzylindole with (diacetoxyiodo)benzene catalysed by palladium acetate. Kinetic experiments suggest that palladation to produce intermediates, such as (60), is rate limiting. " Palladium catalysis, using a Josiphos ligand, has also been used to prepare (V-alkyltacrines, such as (61), by amination of 9-chlorotetrahydro-acridines. " ... 

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