Palladium chloride, reaction with alkenes

The acyl palladium intermediate reacts with alcohols to give esters. In other solvents it decomposes to an acid chloride or reacts with remaining arylpalladium halide to give diaryl ketone. The reaction with alkenes involves addition of the organopalladium intermediate to the alkene, followed by decomposition of the alkylpalladium species by a )8-elimination which is typical of alkylpalladium species ... 

Benzoic acid and substituted benzoic acids are readily thallated by thallium(III) trifluoroacetate. Subsequent reaction with palladium chloride and simple alkenes, allylic or vinyl halides, or vinyl esters result in the formation of isocoumarins eg ... 

Alkenes can be converted to succinic esters by reaction with carbon monoxide, an alcohol, and palladium chloride in the presence of mercuric chloride.1,12 The addition is mostly syn. In similar reaction, both terminal and internal alkynes can be converted to esters of maleic acid. 

The effect of the nature of the electrophile on the stereoselectivity of reactions with substrates containing a terminal alkene and an allylic substituent is dramatically illustrated by some recent results with palladium electrophiles.124 Cyclizations of 3-methyl- or 3-phenyl-5-hydroxyalkenes with palladium catalysts proceed with high selectivity (>9 1) for the 2,3-trans isomer (equation 41).50-124 It is suggested that the steric interactions of the palladium-alkene complex affects the stereochemistry of these cyclizations. In some related cyclizations to form tetrahydropyran products (equation 42 and Table 10), reaction with iodine in the presence of sodium bicarbonate gives a different major diastereomer from cyclization with mercury(II) trifluoroacetate or palladium chloride.123... 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Several examples of the cyclization of indole derivatives with alkenic side chains in the 3-position have been reported.6 In these examples, palladium chloride in combination with silver tetrafluoroborate is the cyclizing agent. The palladium tetrafluoroborate, presumably formed, should be a very reactive palladating species and probably is the reason why these reactions proceed at room temperature, although the mechanism is not yet completely clear. These reactions were worked up reductively (by addition of sodium borohydride) in order to reduce the expected alkenic product or any relatively stable organopalladium complexes that may have been formed (equation 4).6... 

Benzoic acid and its derivatives orthothallate. Reaction of o-carboxyphenylthallium bis(trifluoroace-tate) with palladium chloride and alkenes followed by base treatment yields isocoumarin derivatives (equation 15).41 Cyclization does not occur until base is added in the second step. 

Aryl chlorides Aryl chlorides will substitute alkenes only under very special conditions, and then catalyst turnover numbers are generally not very high. Palladium on charcoal in the presence of triethylphos-phine catalyzes the reaction of chlorobenzene with styrene,58 but the catalyst becomes inactive after one use.59 Examples employing an activated aryl chloride and highly reactive alkenes, such as acrylonitrile, with a palladium acetate-triphenylphosphine catalyst in DMF solution at ISO C with sodium acetate as base react to the extent of only 51% or less.60 Similar results have been reported for the combination of chlorobenzene with styrene in DMF-water at 130 C, using sodium acetate as the base and palladium acetate-diphos as a catalyst.61 Most recently, a method for reacting chlorobenzene with activated alkenes has been claimed where, in addition to the usual palladium dibenzilideneacetone-tri-o-tolylphosphine catalyst, nickel bromide and sodium iodide are added. It is proposed that an equilibrium concentration of iodobenzene is formed from the chlorobenzene-sodium iodide-nickel bromide catalyst and the iodoben-zene then reacts in the palladium-catalyzed alkene substitution. Moderate to good yields were reported from reactions carried out in DMF solution at 140 C 62... 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

The palladium-catalyzed reaction of allyl chloride 11 with the benzyne precursor 104 to produces phenanthrene derivatives 131 is also known [83]. A plausible mechanism for this intermolecular benzyne-benzyne-alkene insertion reaction is shown in Scheme 38. Initially n-allyl palladium chloride la is formed from Pd(0) and 11. Benzyne 106, which is generated from the reaction of CsF and 104, inserted into la to afford the aryl palladium intermediate 132. A second benzyne insertion into 132 produce 133 and subsequent carbopalladation to the alkene afford the cyclized intermediate 134. f>- Iydride elimination from 134 followed by isomerization gave 9-methylphenanthrene 131. 

The mechanism of the Rosenmund reduction has attracted occasional attention. The discovery of Tsuji et al that palladium metal can catalyze the conversion of acyl chlorides (11) into alkenes (13), carbon monoxide and HCl, presumably via intermediates of the form (12 Scheme 5), suggests that (12) may also be an intermediate in the Rosenmund reaction. Consistent with this suggestion is the observation that the unsaturated acyl chloride (14) is converted to phenol by a palladium catalyst.22... 

In combination with the incremental advances concerning reaction conditions in recent years, especially for low-pressure carbonylations, there is a trend toward increasing use of this chemistry to synthesize advanced building blocks. In this respect carboxylation of alkenes with an appropriate alcohol or amine function leads to the formation of lactones or lactams. Thus, cobalt, rhodium, or palladium chloride/copper chloride catalysts convert allyl and homoallyl alcohols or amines to the corresponding butyrolactones or butyrolactams, respectively [15]. 

Decarbonylation of the tricyclic bridgehead acid chloride (29) with a palladium catalyst at 130 C in the presence of tri-n-butylamine gives exclusively the disubstituted alkene (30) in essentially quantitative yield." Under these conditions none of the bridgehead alkene is obtained, but it is assumed that this is an intermediate in the reaction. 

Cyclopropanation reactions with these catalysts are typically carried out with 0.5-2 mol% (with respect to the diazo compound) of catalyst and a five- to tenfold excess of alkene. Under these conditions, the formation of formal carbene dimers [e.g. diethyl ( )-but-2-enedioate and (Z)-but-2-enedioate from ethyl diazoacetate], arising from the competition between alkene and the metal-carbene intermediate for the diazo compound, can be largely suppressed. It has been shown, however, that the control of the addition rate of the diazoacetic ester has no effect on the cyclopropane yield with (dibenzonitrile)palladium(II) chloride as catalyst, in contrast to tetraacetatodirhodium, Rhg(CO)ig, and CuCl P(OR)3. ... 

Photochemical decomposition of diazo(trimethylsilyl)methane (1) in the presence of alkenes has not been thoroughly investigated (see Houben-Weyl Vol. E19b, p 1415). The available experimental data [trimethylsilylcyclopropane (17% yield) and la,2a,3j8-2,3-dimethyl-l-trimethylsilylcyclopropane (23% yield)] indicate that cyclopropanation occurs only in low yield with ethene and ( )-but-2-ene. In both cases the formal carbene dimer is the main product. In reactions with other alkenes, such as 2,3-dimethylbut-2-ene, tetrafluoroethene or hexafluoro-propene, no cyclopropanes could be detected.The transition-metal-catalyzed decomposition of diazo(trimethylsilyl)methane (1) has been applied to the synthesis of many different silicon-substituted cyclopropanes (see Table 3 and Houben-Weyl Vol.E19b, p 1415) 3.20a,b,2i.25 ( iQp. per(I) chloride has been most commonly used for carbene transfer to ethyl-substituted alkenes, cycloalkenes, styrene, and related arylalkenes. For the cyclopropanation of acyl-substituted alkenes, palladium(II) chloride is the catalyst of choice, while palladium(II) acetate was less efficient, and copper(I) chloride, copper(II) sulfate and rhodium(II) acetate dimer were totally unproductive. The cyclopropanation of ( )-but-2-ene represents a unique... 

The selectivity of palladium and gold for alkene oxidation to aldehydes 28,29,170) was attributed initially to adsorption strength. However, electrooxidation in the presence of palladium ions indicates possible homogeneous alkene insertion, similar to the Wacker process 304). Homogeneous reaction is also involved in redox oxidations of hydrocarbons. In this case, the nature of the metal ions is expected to control selectivity. Indeed, toluene yields 20% benzaldehyde in electrolytes containing Ce salts, while oxidation proceeds to benzoic acid with Cr redox catalysts 311). In addition, the concentration of redox catalysts appears to affect yields in nonelectrochemical oxidation of ethylene large amounts of palladium chloride promote butene formation at the expense of acetaldehyde 312). Finally, the role of the electrolyte and solvent should not be ignored. For instance, electrooxidation of ethylene on carbon, in aqueous solution of acetic acid yields acetaldehyde 313) in the... 

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