Carbon monoxide allylic halides

Carbon monoxide is essential for the present reaction (vide supra), and no reaction occurred at all under an argon atmosphere. The addition of base is also indispensable, and EtsN is the most effective base, which should be a hydrogen source for the products. Allylic carbonates and allylic halides did not give products in good yield. 

It is generally assumed that the Lewis acid in 3 decreases the charge on the metal, i.e., increases its electrophilicity. The removal of charge from the nickel allows additional electron donors to coordinate to the nickel atom, and reaction with, for example, 2 moles of carbon monoxide or 1 mole of 1,5-cyclooctadiene (COD) gives the insoluble, catalytically inactive and presumably ionic complexes 7 and 8. In contrast, 7r-allyl-nickel halides (1) add only 1 mole of carbon monoxide while they do not react with COD (52). 

The carbonylation was explained by the following mechanism. Formation of dimeric 7r-allylic complex 20 from two moles of butadiene and the halide-free palladium species is followed by carbon monoxide insertion at the allylic position to give an acyl palladium complex which then collapses to give 3,8-nonadienoate by the attack of alcohol with regeneration of the zero-valent palladium phosphine complex. When halide ion is coordinated to palladium, the formation of the above dimeric 7r-allylic complex 20 is not possible, and only monomeric 7r-allylic complex 74 is formed. Carbon monoxide insertion then gives 3-pentenoate (72). 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

This reaction involves the two reactants carbon monoxide and alcohol and produces esters, or lactones. The starting material, which will be considered here, is an alkene or an alkyne but it is also possible to start from activated halides (aryl- or allyl- iodides and bromides) to produce the same kind of organic products. 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

The simple procedure for the carbonylation of allyl halides has been extended in the high yielding solid-liquid two-phase conversion of allyl phosphates into amides (60-80%) under the influence of a rhodium carbonyl cluster in the presence of primary or secondary amines (Scheme 8.8). A secondary product of the reaction is the allylamine, the concentration of which increases as the pressure of the carbon monoxide is reduced, such that it is the sole product (ca. 80%) in the absence of carbon monoxide [28],... 

Numerous metal-catalyzed reactions of organic halides with carbon monoxide and olefins, acetylenes, aldehydes, etc., have been carried out (21). Only two of these, however, appear to have been developed into generally useful reactions. One is the reaction of allylic halides with carbon monoxide and acetylene in alcoholic solution with a nickel catalyst (22,23). This reaction produces cis-2,5-hexadienoate esters at atmospheric pressure in good yields ... 

A particularly simple variation of this reaction has been developed (47, 48) in which the catalytic nickel species is formed in situ by reduction of nickel chloride with a manganese -iron alloy in the presence of thiourea. Allyl halide is added and at the same time acetylene and carbon monoxide are bubbled through the methanolic solution. Conversion is almost complete and yields of ar-methyl-2,5-dienoate of up to 80% have been claimed. 

Under conditions similar to those for allyl halides, 1,4-dichlorobutene reacts with nickel carbonyl to give butadiene. However, a double insertion of acetylene and carbon monoxide can be successfully carried out using 4-chloro-2-buten-l-ol and generating hydrogen halide in situ with a weak acid inorganic halide combination, e.g., NaBr-H3P04 (58). 

Benzyl halides have been reported to react with nickel carbonyl to give both coupling and carbonylation (59). Carbonylation is the principal reaction in polar nonaromatic solvents, giving ethyl phenylacetate in ethanol, and bibenzyl ketone in DMF. The reaction course is probably similar to that of allylic halides. Pentafluorophenyl iodide gives a mixture of coupled product and decafluorobenzophenone. A radical mechanism has been proposed (60). Aromatic iodides are readily carbonylated by nickel carbonyl to give esters in alcoholic solvents or diketones in ethereal solvent (57). Mixtures of carbon monoxide and acetylene react less readily with iodobenzene, and it is only at 320° C and 30 atm pressure that a high yield of benzoyl propionate can be obtained (61). Under the reaction conditions used, the... 

Nadal and colleagues recently reported a Ni-catalyzed carbonylative Pauson-Khand-like [2+2+1] cycloaddition of allyl halides and alkynes in the presence of carbon monoxide and iron as the stoichiometric reducing agent [148]. The reaction was proposed to occur via reductively generated Ni(I)-radical like species free radicals were, however, considered unlikely. 

Meerifield, J. H., Godschal, J. P., Stille, J. K. Synthesis of unsymmetrical diallyl ketones the palladium-catalyzed coupling of allyl halides with allyltin reagents in the presence of carbon monoxide. Organometallics 3, 1108-1112. 

A more versatile palladium-catalyzed formylation of organic halides takes place using tributyltin hydride and carbon monoxide (equation 7). The reaction works for a variety of substrates — aryl, benzyl and vinyl iodides, vinyl triflates and allyl halides. Reaction conditions are mild (1-3 bar CO, 50 °C), and a variety of functional groups can be tolerated. With unsymmetrical allyl halides formylation is regio-selective, taking place at the less-substituted allylic position with retention of geometry at the allylic double bond. 

Alkenyl, allyl, and aryl halides undergo oxidative addition to Pd° complexes to form alkenyl-, allyl-, and aryl-palladium a-complexes which then react with carbon monoxide, alkenes and alkynes. 

The reactions of allyl, alkenyl, and arylstannanes with allyl, alkenyl, and aryl halides or triflates proceed in the presence of palladium catalysts to give the cross-coupling products (eq (107)) [102]. In the reaction of alkenylstannanes, their configuration is generally retained. If these reactions are carried out in an atmosphere of carbon monoxide, the corresponding ketones are obtained (eq (108)) [103]. 

In general for carbonylations, palladium as catalyst metal is preferable to nickel with respect of catalyst efficiency. Thus, Okano, Kiji, and co-workers described some other efficient palladium-catalyzed carbonylations of allyl chloride and substituted allyl halides (Eqs. 5-10). In greater detail, the water-soluble palladium complex PdCl2[Ph2P(w-C6H4S03Na)]2 has been used in a two-phase system (e.g., aqueous NaOH/benzene medium) at atmospheric carbon monoxide pressure, giving 3-butenoic acids [20], In the carbonylation of allyl chloride a mixture of 2-bute-noic acid, which was formed by base-catalyzed isomerization, and 3-butenoic acid was obtained in up to 90% yield (TON = 135), albeit at moderate selectivity (24 76). Clearly, the isomerization depends on the concentration of the base and was therefore suppressed by a method of continuous addition to the aqueous medium. 

This alternative to the Friedel-Crafts reaction, extensively developed by Stille and coworkers, is particularly important, since the reaction conditions are essentially neutral, and so provides a method for acylation of compounds containing an acid-sensitive functionality which would preclude the use of the Friedel-Crafts reaction. Reaction temperatures are often below 100 C, and high (1000-fold) turnovers of the catalyst have been achieved. Solvents employed include chloroform, toluene, and, on occasions, HMPA. Some reactions have been carried out under an atmosphere of carbon monoxide to prevent excessive decarbonylation of the acyl palladium intermediate. Indeed, carbonylative coupling of alkenylstannanes with allyl halides in the presence of carbon monoxide ca. 3 atm or greater 1 atm =101 kPa) offers an alternative to the Friedel-Crafts acylation, ketones being formed by the reaction of the stannane with the acyl species formed by carbon monoxide insertion into the allyl palladium intermediate. ... 

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