Palladium-catalyzed reactions carbonyls

Later, a nickel-catalyzed cascade conversion of propargyl halides and propargyl alcohol into a pyrone in water was reported. The reaction involved a carbonylation by CO and a cyanation by KCN (Eq. 4.55).96 Recently, Gabriele et al. explored a facile synthesis of maleic acids by palladium catalyzed-oxidative carbonylation of terminal alkynes in aqueous DME (1,2-dimethoxyethane) (Eq. 4.56).97... 

The study on 2,7-di-rerf-butylthiepin has recently been extended to explore more simply substituted thiepins 58). The palladium-catalyzed reaction of the diazo compound 107 lacking a 4-methyl substituent gives exclusively the exo-methylene compound 108 whereas the acid-catalyzed reaction of the same precursor 107 resulted in the formation of 2,7-di-/er/-butyl-4-ethoxycarbonylthiepin (109)58). Due to the substantial thermal stability of 109 it is possible to transform the ethoxy-carbonyl group into the hydroxymethyl (110), trimethylsilyloxymethyl (111) and formyl group (112)58). 

The palladium-catalyzed Heck carbonylation reaction is a powerful means of generating amides, esters, and carboxylic acids from aryl halides or pseudohalides [28]. The development of rapid, reliable, and convenient procedures for the introduction of carbonyl groups is important for the development of high throughput chemistry in general and high-speed microwave-mediated chemistry in particular. Unfortunately, the traditional method of introducing carbon monoxide into a reaction mixture via a balloon or gas tube is not practical because of the special requirements of microwave synthesis. 

For the preparation of a-ketoamides, palladium-catalyzed double carbonylation of aryl halides with carbon monoxide and secondary amines is also a useful reaction Kobayashi, T. Tanaka, M. J. Organomet. Chem. 1982, 233, C64 Ozawa, F. Soyama, H. Yamamoto, T. Yamamoto, A. Tetrahedron Lett. 1982, 23, 3383. 

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

The mechanism of the Zn chloride-assisted, palladium-catalyzed reaction of allyl acetate (456) with carbonyl compounds (457) has been proposed [434]. The reaction involves electroreduction of a Pd(II) complex to a Pd(0) complex, oxidative addition of the allyl acetate to the Pd(0) complex, and Zn(II)/Pd(II) transmetallation leading to an allylzinc reagent, which would react with (457) to give homoallyl alcohols (458) and (459) (Scheme 157). Substituted -lactones are electrosynthesized by the Reformatsky reaction of ketones and ethyl a-bromobutyrate, using a sacrificial Zn anode in 35 92% yield [542]. The effect of cathode materials involving Zn, C, Pt, Ni, and so on, has been investigated for the electrochemical allylation of acetone [543]. 

Much less attention has been focused on carbonylation reactions in ionic liquids. The biphasic palladium-catalyzed alkoxy carbonylation of styrene. Scheme 2, in [bmim][BF4]—cyclohexane has been reported. ... 

Carbon monoxide, a common ligand in organometallic chemistry, is known to insert into palladium-carbon bonds readily. This feature of the metal is frequently utilized when palladium catalyzed reactions are run in the presence of CO. The products of such reactions, also known as carbonylative couplings, incorporate a carbonyl group between the coupling partners. 

Many such activated acyl derivatives have been developed, and the field has been reviewed [7-9]. The most commonly used irreversible acyl donors are various types of vinyl esters. During the acylation of the enzyme, vinyl alcohols are liberated, which rapidly tautomerize to non-nucleophilic carbonyl compounds (Scheme 4.5). The acyl-enzyme then reacts with the racemic nucleophile (e.g., an alcohol or amine). Many vinyl esters and isopropenyl acetate are commercially available, and others can be made from vinyl and isopropenyl acetate by Lewis acid- or palladium-catalyzed reactions with acids [10-12] or from transition metal-catalyzed additions to acetylenes [13-15]. If ethoxyacetylene is used in such reactions, R1 in the resulting acyl donor will be OEt (Scheme 4.5), and hence the end product from the acyl donor leaving group will be the innocuous ethyl acetate [16]. Other frequently used acylation agents that act as more or less irreversible acyl donors are the easily prepared 2,2,2-trifluoro- and 2,2,2-trichloro-ethyl esters [17-23]. Less frequently used are oxime esters and cyanomethyl ester [7]. S-ethyl thioesters such as the thiooctanoate has also been used, and here the ethanethiol formed is allowed to evaporate to displace the equilibrium [24, 25]. Some anhydrides can also serve as irreversible acyl donors. 

Palladium catalyzes the carbonylation of allylic, vinylic, benzylic, and aromatic halides in alcohols to form esters under conditions similar to those required by the nickel carbonyl catalyst (11). The palladium-catalyzed reaction offers the advantage of not requiring the use of highly toxic and volatile nickel carbonyl, and perhaps higher catalyst activity, although accurate comparisons have not been made. Like the nickel reaction, the palladium reaction... 

The mechanism of the palladium-catalyzed reaction is similar to that of the allyl chloride-nickel carbonyl reaction described above, but more complex, at least when phosphine ligands are present (14). The first step is believed... 

Fig. 43 Palladium-catalyzed tandem carbonylation/Suzuki coupling reactions...

The reaction of an aUcene (or aUcyne), CO, and H2O to directly produce a carboxylic acid is called Reppe carbony-lation chemistry or, more recently, hydrocarboxylation (see Reppe Reaction). An excellent review of palladium-catalyzed Reppe carbonylation systems has been published recently by Kiss, and coverage of this important material will not be repeated here. This catalytic reaction has been known for quite some time, although the stoichiometric Ni(CO)4-based carbonylation of acetylene was the first commercial carbonylation process implemented (equation 13). The extreme toxicity of Ni(CO)4, however, has limited practical applications (see Nickel Organometallic Chemistry). Co, Rh, and Pd catalysts have certainly replaced Ni(CO)4 in smaller-scale laboratory reactions, though for historical reasons a number of the fim-damental mechanisms discussed in this section are based on Ni(CO)4. 

Palladium-catalyzed carbonylation reactions have assumed increasing importance over the last 30 years, particularly for smaUer-scale laboratory and fine chemical syntheses (see Palladium Organometallic Chemistry). There is an enormous amount of work on palladium-catalyzed reactions, and it would be impossible to cite many specific examples. It is possible, however, to generalize the mechanism for producing... 

A new metal-catalyzed exocyclic carbonylation of cycloimino esters 184 was reported. The reaction proceeded without HI in relatively mild conditions affording the expected N-acyl oxazolidin-2-ones 185 <03OL3955>. An improved procedure for the palladium catalyzed oxidative carbonylation of P-aminoalcohols to oxazolidin-2-ones was published <03JOC601>. 

There are interesting transition metal-catalyzed-reactions that lead to aryl amides. The use of POCI3 and DMF, with a palladium catalyst, converts aryl iodides to benzamides. A palladium-catalyzed reaction of aryl hahdes and for-mamide leads to benzamide derivatives. Carbonylation is another method that generates amides. When an aryl iodide was treated with a secondary amine and Mo(CO)e, in the presence of 3 equivalents of DBU, 10% Pd(OAc)2, with micro-wave irradiation at 100°C, the corresponding benzamide was obtained. 

An alternative strategy for achieving asymmetric control may be by covalent attachment of a chiral auxiliary to the carbenoid. This strategy has so far met with rather limited success in cyclopropanation reactions (see eq. (3) for a similar palladium-catalyzed reaction). However, the use of a-hydroxy esters as chiral auxiliaries with stabilized rhodium(II) vinylcarbenoids allowed entry into both series of enantiomeric vinylcyclopropanes with predictable stereochemistry. Optical yields are fair to excellent [14] and the outcome of the reaction was rationalized on the basis of interactions between the carbonyl oxygen of the chiral auxiliary and the carbenoid carbon. The strategy led to an efficient synthesis of optically active hydroxy vitamin D3 ring A [28]. 

Palladium-catalyzed double carbonylations of aromatic halides have also been studied (equation 63). ° As might be expected, higher pressure is favorable for both reaction rate and selectivity. Selectivity for the formation of keto esters is also maximized by the use of sterically hindered alcohols and solvents of low polarity. 

Alfhough direct nucleophilic addition is limited because of the low nucleophilicity of fhe fluoride ion, a palladium-catalyzed reaction enables the weak nucleophile to participate fhe addition reaction. In the presence of cesium fluoride, palladium-catalyzed carbonylation of an aryl halide gives fhe acyl fluoride in good yield (Scheme 2.5) [8]. 

The carbonylation of butadiene, readily available from petroleum sources, yields a dicarbonylated adduct and dimer-carbonylated product, both desirable from a commercial standpoint. Palladium-catalyzed reactions yield monocarbonylated ... 

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