Oxidative, carbonylation

Oxidative carbonylation of alkenes is a unique reaction of Pd(II). Three types of oxidative carbonylation to give -substituted acid derivatives 130, a, -unsaturated esters 132 and succinate derivatives 134 are known, which can be understood by the following mechanism. Palladation of alkenes with PdX2, followed by CO insertion, generates the acylpalladium intermediate 129 whose reductive elimination affords -substituted carboxylic acid derivatives 130 (path a). Reaction in alcohol in the presence of a base starts by the formation of the alkoxycarbonylpalladium 128. Carbopalladation of alkene with 128 generates 131. Then y3-H elimination of the intermediate 131 yields the a-unsaturated ester 132 (path b). Further CO insertion to 131 gives the acylpalladium intermediate 133 and its alcoholysis yields the succinate derivative 134 (path c). Formation of the jS-alkoxy ester 130 (X-OR) is regarded as nucleophilic substitution of Pd-X in 131 with alcohols. 

The first report of the oxidative carbonylation is reaction of alkenes with CO in benzene in the presence of PdCl2 to afford the /3-chloroacyl chloride 135 (path a) [14,55], 

Hydrocarbonylation of alkenes to give the saturated esters 136 and 137 is catalyzed by Pd(0) (see Chapter 8.1) [56]. It should be pointed out that the hydrocarbonylation is clearly different mechanistically from the oxidative carbonylation, which is promoted by Pd(II) to produce 130, 132 and 134. 

Carbonylation of alkenes having an amino or hydroxy group (AH or BH = OH or NHR) 140, 142 and 144 offers interesting synthetic methods for cyclic compounds. The 4-pentenylamine or alcohol 140 is converted to 141 via amino or oxypalladation, followed by carbonylation. The amino alcohol 142 gives 143 by palladation and carbonylation by path a. The homoallylic amine or alcohol 144 is converted to lactone or lactam ester 145 by path c [60]. 

Aminocarbonylation of A -4-pentenyl-A -methylurea (146) gave 147 smoothly in the presence of PdCl2, CuCl2 and O2 [61]. Aminocarbonylation of the unsaturated diamine derivative 148 is chemoselective. In the presence of sodium acetate and methyl orthoformate, aminopalladation of the tosylamide took place selectively to Erfford 150 via 149. On the other hand, selective reaction of the carbamate occurred to give 151 in the absence of sodium acetate [62], 

As a unique reaction of Pd(II), the oxidative carbonylation of alkenes is possible with Pd(ll) salts. Oxidative carbonylation is mechanistically different from the hydrocarboxylation of alkenes catalyzed by Pd(0), which is treated in Chapter 4, Section 7.1. The oxidative carbonylation in alcohol can be understood in the following way. The reaction starts by the formation of the alkoxy-carbonylpalladium 218. Carbopalladation of alkene (alkene insertion) with 218 gives 219. Then elimination of /3-hydrogen of this intermediate 219 proceeds to 

The first report of oxidative carbonylation is the reaction of alkenes with CO in benzene in the presence of PdCh to afford the /3-chloroacyl chloride 224[12,206]. The oxidative carbonylation of alkene in alcohol gives the q, f3-unsaturated ester 225 and /3-alkoxy ester 226 by monocarbonylation, and succinate 111 by dicarbonylation depending on the reaction conditions[207-209]. The scope of the reaction has been studied[210]. Succinate formation takes 

The dicarboxylation of cyclic alkenes is a useful reaction. All-c.vo-methyl-7-oxabicyclo(2.2.1]heptane-2,3,5,6-tetracarboxylate (233) was prepared from the cyclic alkene 232 using Pd on carbon and CuCh in MeOH at room temperature with high diastereoselectivity[216]. The dicarbonylation of cyclopentene 

The carbonylation of COD PdCl2 complex in aqueous sodium acetate produces /rui7x-2-hydroxy-5-cyclooctenecarboxylic acid /i-lactone (240). The lactone is obtained in 79% yield directly by the carbonylation of the COD complex in aqueous sodium acetate solution[220]. /i-Propiolactone (241) is obtained in 72% yield by the reaction of the PdCC complex of ethylene with CO and water in MeCN at —20 C. /3-Propiolactone synthesis can be carried out with a catalytic amount of PdCC and a stoichiometric amount of CuCl2[221]. 

The carbonylation of alkene in AcOH-acetic anhydride in the presence of NaCl affords the /9-acetoxycarboxylic anhydride 242 in good yields and the method offers a good synthetic method for / -hydroxycarboxylic acid 243[222], 

The /f-alkoxy ester 111 is formed by nucleophilic substitution of 114 with alkoxide. Formation of 109, the esters 111, and 112 can be regarded as the nucleophilic addition to alkenes promoted by Pd(II). 

Scope of oxidative carbonylation has been studied [83]. The synthesis of acrylic acid or its ester (116) from ethylene has been investigated in AcOH from the standpoint of its commercial production [84]. The carbonylation of styrene is a promising commercial process for cinnamate (117) [80,85,86]. Succinate formation occurs at room temperature and 1 atm of CO using Pd on carbon as a catalyst in the presence of an excess of CuCl2, although the reaction is slow (100% conversion after 9 days) [87], 

Asymmetric carbonylation of styrene with Pd(acac)2 and benzoquinone in the presence of TsOH using 2,2 -dimethoxy-6,6/-bis(diphenylphosphino)-biphenyl (119) as a chiral ligand gave dimethyl phenylsuccinate (118) with 93% ee, although yield was not satisfactory, showing that phosphine coordination influences the stereochemical course of the oxidative carbonylation with Pd(II) salts [88]. 

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Reactions of another class are catalyzed by Pd(II) compounds which act as Lewis acids, and are treated in Chapter 5 and partly in Chapter 4. From the above-mentioned explanation, the reactions catalyzed by Pd(0) and Pd(II) are clearly different mechanistically. In this book the stoichiometric and catalytic reactions are classified further according to reacting substrates. However, this classification has some problems, viz. it leads to separate treatment of some unit reactions in different chapters. The carbonylation of alkenes is an example. Oxidative carbonylation of alkenes is treated in Chapter 3 and hydrocar-bonylation in Chapter 4. 

Benzoic acid and naphthoic acid are formed by the oxidative carbonylation by use of Pd(OAc)2 in AcOH. t-Bu02H and allyl chloride are used as reoxidants. Addition of phenanthroline gives a favorable effect[360], Furan and thiophene are also carbonylated selectively at the 2-position[361,362]. fndole-3-carboxylic acid is prepared by the carboxylation of 1-acetylindole using Pd(OAc)2 and peroxodisulfate (Na2S208)[362aj. Benzoic acid derivatives are obtained by the reaction of benzene derivatives with sodium palladium mal-onate in refluxing AcOH[363]. 

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

Aconitatc was obtained as a minor product in the carbonylation of propar-gyl alcohol[479]. However, in the two-step synthesis of methyl aconitate (536) from propargyl alcohol in 70% overall yield, the first step is the oxidative carbonylation under CO and air using Pdli and KI to giNe dimethyl hydro-xymethylbutenedioate (535), which is carbonylated further to give trimethyl aconitate (536) by u.sc of [Pd(Tu)4jl2 as a catalyst[480]. 

Oxidative carbonylation can sometimes be achieved even in the absence of any oxidizing agent. As an example, unexpectedly diphenylcrotonolactone (537) was obtained as a major product by the carbonylation of diphenylaeety-... 

As an application of maleate formation, the carbonylation of silylated 3-butyn-l-ol affords the 7-butyrolactone 539[482], Oxidative carbonylation is possible via mercuration of alkynes and subsequent Lransmetallation with Pd(II) under a CO atmosphere. For example, chloromercuration of propargyl alcohol and treatment with PdCF (1 equiv.) under 1 atm of CO in THF produced the /3-chlorobutenolide 540 in 96% yield[483]. Dimethyl phenylinale-ate is obtained by the reaction of phenylacetylene, CO, PdCU, and HgCl2 in MeOH[484,485]. 

Carbonylation of the complex 548 proceeds in ethanol gives ethyl 3-chloro-3-butenoate (554), The lactone 555 and the two esters 556 and 557 are obtained by carbonylation of the dimeric complex 549. The oxidative carbonylation of allene in ethanol with PdCl2 gives ethyl itacoante (558), although the yield is low[498]. 

The catalytic oxidative carbonylation of allene with PdCb and CuCh in MeOH affords methyl a-methoxymethacrylate (559)[499]. The intramolecular oxidative aminocarbonylation of the 6-aminoallene 560 affords the unsaturated J-amino ester 561. The reaction has been applied to the enantioselective synthesis of pumiliotoxin (562)[500]. A similar intramolecular oxycarbonyla-tion of 6-hydroxyallenes affords 2-(2-tetrahydrofuranyl)acrylates[501]. 

Oxidative carbonylation of alcohols with PdCh affords the carbonate 572 and oxalate 573(512-514]. The selectivity of the mono- and dicarbonylation depends on the CO pressure and reaction conditions. In order to make the reaction catalytic, Cu(II) and Fe(III) salts are used. Under these conditions, water is formed and orthoformate is added in order to trap the water. Di-/-butyl peroxide is also used for catalytic oxidative carbonylation to give carbonates and oxalates in the presence of 2,6-dimetliylpyridine(515]. 

The alkylurea 576 and oxamide 577 are formed by oxidative carbonylation of amines under CO pressure using Pd/C as a catalyst[518]. The urea formation proceeds under atmospheric pressure using PdCh and CuCl2[519]. The mono-and double carbonylations of / -aminoethanol (578 and 579) afford the cyclic carbamate (oxazolidinones) 580 and oxamide (morpholinediones) 581 [520,521]. 

Carbamates are produced by the oxidative carbonylation of amines in alcohol, and active research on the commercial production of carbamates as a precursor of isoyanates based on this reaction has been carried out. As an example, ethyl phenylcarbamate (582) is produced in a high yield (95%) with... 

As an e.xtension of the oxidative carbonylation with alkyl nitrites, malonate can be prepared by the oxidative carbonylation of ketene (583)[524], Also, the acetonedicarboxylate 585 is prepared by the Pd-catalyzed, alkyl nitrite-mediated oxidative carbonylation of diketene (584)[525],... 

Although turnover of the catalyst is low, even unreactive cyclohexane[526] and its derivatives are oxidatively carbonylated to cyclohexanecarboxylic acid using KiS Og as a reoxidant in 565% yield based on Pd(II)[527]. Similarly, methane and propane are converted into acetic acid in 1520% yield based on Pd(II) and butyric acid in 5500% yield [528],... 

Using a catalyst system of PdCl2, CuCH, HCl, and O2, the internal alkyne 20 is carbonylated at room temperature and 1 atm to give unsaturated esters[19]. This apparently oxidizing system leads to non-oxidative cu-hydroesterilica-tion. With terminal alkynes, however, oxidative carbonylation is observed. 

Carbonylation of the tetrasubstituted bispropargyiic amine 23 using PdCP and thiourea under mild conditions affords the carboxylated pyrrolidine derivatives 24a and b in good yields. Thiourea is regarded as effective for the oxidative carbonylation of alkynes, but no oxidative carbonylation was observed in this case[21]. 

Oxidative bleaching Oxidative carbonylation Oxidative coupling... 

Oxidative Carbonylation of Ethylene—Elimination of Alcohol from p-Alkoxypropionates. Spectacular progress in the 1970s led to the rapid development of organotransition-metal chemistry, particularly to catalyze olefin reactions (93,94). A number of patents have been issued (28,95—97) for the oxidative carbonylation of ethylene to provide acryUc acid and esters. The procedure is based on the palladium catalyzed carbonylation of ethylene in the Hquid phase at temperatures of 50—200°C. Esters are formed when alcohols are included. Anhydrous conditions are desirable to minimize the formation of by-products including acetaldehyde and carbon dioxide (see Acetaldehyde). 

The elimination of alcohol from P-alkoxypropionates can also be carried out by passing the alkyl P-alkoxypropionate at 200—400°C over metal phosphates, sihcates, metal oxide catalysts (99), or base-treated zeoHtes (98). In addition to the route via oxidative carbonylation of ethylene, alkyl P-alkoxypropionates can be prepared by reaction of dialkoxy methane and ketene (100). 

The oxidative carbonylation of styrene with carbon monoxide, oxygen, and an aUphatic alcohol in the presence of a palladium salt, a copper salt, and sodium propionate also provides the requisite cinnamate. 

Metathesis is the rupture and reformation of carbon-carbon bonds—for example, of propylene into ethylene plus butene. Catalysts are oxides, carbonyls, or sulfides of Mo, W, or Re. 

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

M-NHC catalysts in this area. Metal catalysed carbonylation also provides an alternative synthetic ronte to the prodnction of materials that traditionally reqnire highly toxic precnrsors, like phosgene. This section discnsses carbonylation of aryl hahdes, oxidative carbonylation of phenolic and amino componnds, carbonylation of aryl diazoninm ions, alcohol carbonylation, carbonylative amidation, and copolymerisation of ethylene and CO. 

Oxidative carbonylation generates a number of important compounds and materials such as ureas, carbamates, 2-oxazolidinones, and aromatic polycarbonates. The [CuX(IPr)] complexes 38-X (X = Cl, Br, I) were tested as catalysts for the oxidative carbonylation of amino alcohols by Xia and co-workers [43]. Complex 38-1 is the first catalyst to selectively prepare ureas, carbamates, and 2-oxazolidinones without any additives. The important findings were the identity of the counterion and that the presence of the NHC ligand influenced the conversions. 2-Oxazohdinones were formed from primary amino alcohols in 86-96% yield. Complex 38-1 also catalysed the oxidative carbonylation of primary amines to ureas and carbamates. n-Propylamine, n-butylamine, and t-butylamine were transformed into the... 

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