Transition Metal-Catalyzed Carbonylations

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

In most transition metal-catalyzed reactions, one of the carbene substituents is a carbonyl group, which further enhances the electrophilicity of the intermediate. There are two general mechanisms that can be considered for cyclopropane formation. One involves formation of a four-membered ring intermediate that incorporates the metal. The alternative represents an electrophilic attack giving a polar species that undergoes 1,3-bond formation. 

Transition-metal catalyzed carbonylation of 1-perfluoroalkyl-substituted 2-iodoalkanes has been carried out in aqueous media to give carboxylic acids with a perfluoroalkyl substituent at the (J> position (Eq. 6.28).61... 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

In earlier studies the in vitro transition metal-catalyzed oxidation of proteins and the interaction of proteins with free radicals have been studied. In 1983, Levine [1] showed that the oxidative inactivation of enzymes and the oxidative modification of proteins resulted in the formation of protein carbonyl derivatives. These derivatives easily react with dinitrophenyl-hydrazine (DNPH) to form protein hydrazones, which were used for the detection of protein carbonyl content. Using this method and spin-trapping with PBN, it has been demonstrated [2,3] that protein oxidation and inactivation of glutamine synthetase (a key enzyme in the regulation of amino acid metabolism and the brain L-glutamate and y-aminobutyric acid levels) were sharply enhanced during ischemia- and reperfusion-induced injury in gerbil brain. 

This chapter mainly treats transition metal-catalyzed direct functionalization of carbon-hydrogen bonds in organic compounds. This methodology is emphasized by focusing on important functionalizations for synthetic use. The contents reviewed here are as follows (i) alkylation of C-H bonds, (ii) alkenylation of C-H bonds, (iii) arylation of C-H bonds, (iv) carbonylation of C-H bonds, (v) hydroxylation and the related reactions, and (vi) other reactions and applications. 

These reactions are covered in other chapters of Volume 11 (Chapters 11.06 and 11.07). This part deals only with examples which are in connection with other sections of this chapter. Additions of metallocarbenoids to unsaturated partners have been extensively studied. Most of the initial studies have involved the transition metal-catalyzed decomposition of cr-carbonyl diazo compounds.163,164 Three main reaction modes of metallocarbenoids derived from a-carbonyl diazo precursor are (i) addition to an unsaturated C-C bond (olefin or alkyne), (ii) C-H insertion, and (iii) formation of an ylid (carbonyl or onium).1 5 These reactions have been applied to the total synthesis of natural... 

For a review encompassing the transition metal-catalyzed reductive coupling of carbonyl compounds, see Avalos, M. Babiano, R. Gintas, P. ... 

In conclusion, the ene reaction has undergone a synthetic renaissance with the advent of Lewis acid and transition metal-catalyzed protocols. The carbonyl-ene, imino-ene, and Alder-ene reactions have all experienced tremendous growth due to the mild conditions in which these reactions can be performed, the high functional group compatibility and high stereoselectivity. As a confirmation of the synthetic utility of the ene reaction, there are many applications to natural product synthesis, and some of these are highlighted in Section 10.12.6. Finally, it should be mentioned that these catalyzed ene reactions are still in their infancy, so much remains to be learned. 

Transition-metal carbonyls, 16 58 Transition metal catalysts, 20 151-152 Transition-metal-catalyzed microwave-assisted reactions, 16 552 Transition metal-catalyzed reactions in ionic liquids, 26 878-897 Transition-metal clusters, structure of,... 

Abstract Development in the field of transition metal-catalyzed carbonylation of epoxides is reviewed. The reaction is an efficient method to synthesize a wide range of / -hydroxy carbonyl compounds such as small synthetic synthons and polymeric materials. The reaction modes featured in this chapter are ring-expansion carbonylation, alternating copolymerization, formylation, alkoxycarbonylation, and aminocarbonylation. 

Direct electrochemical allylation can be performed with some carbonyl compounds.Transition metal catalyzed couplings are however more efficient, notably in reactions involving ketones. 

Hydrogen transfer reactions from an alcohol to a ketone (typically acetone) to produce a carbonyl compound (the so-caUed Oppenauer-type oxidation ) can be performed under mild and low-toxicity conditions, and with high selectivity when compared to conventional methods for oxidation using chromium and manganese reagents. While the traditional Oppenauer oxidation using aluminum alkoxide is accompanied by various side reactions, several transition-metal-catalyzed Oppenauer-type oxidations have been reported recently [27-29]. However, most of these are limited to the oxidation of secondary alcohols to ketones. 

Transition-metal-catalyzed carbonylations are of great importance in organic synthesis as a powerful tool to prepare a variety of carbony compounds. Among them, hydroformylation has been most extensively studied not only in the laboratory but also in industry. Industrial production of alkanals from 1-alkenes... 

This review deals with the recent developments in the transition metal-catalyzed carbonylation reaction, especially hydroformylation, hydrocarbonylation, and oxidative hydrocarbonylation reactions of olefins, referring to literature since 1994. Because of the importance of carbonyl functionality in organic chemistry and the ideal atom efficiency of... 

The most notable point of this reaction is that the internal sp-c xhon is selectively carbonylated to form (Z)-14a predominantly, although the ZjE ratio is likely to depend on reaction temperature, time, and catalyst precursor. It is revealed that the stereochemistry of the transition metal-catalyzed addition to alkynes is intrinsically cis. Isomerization from (Z)-14a to ( )-14a proceeds as an independent event from silylformylation. This feature sharply contrasts to the results observed in hydrosilylation of 13 with Me2PhSiH (Equation (3)). ... 

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. 

CASE STUDY TRANSITION-METAL CATALYZED CARBONYLATION... 

Case Study Transition-Metal Catalyzed Carbonylation of Methanol... 

Naturally, the ideal source of starting materials for homoleptic metal isocyanide compounds is via metal carbonyl complexes, but previously only with the two carbonyls Ni(CO)4 (24) and Co2(CO)g (25) has direct substitution of all carbonyl groups been effected. Recently, however, remarkable discoveries by Coville and co-workers (26-31) on the transition-metal-catalyzed substitution of carbonyl groups in monomeric and cluster compounds have shown that Fe(CNR)s, Mo(CNR)6, and Ir4(CO)5(CNR)7 (32) can be prepared in high yield by stepwise substitution from the parent carbonyl. 

The transition metal-catalyzed carbonylation reaction is an important pathway to introduce an extra carbon atom in the heterocyclic ring. Lu and Alper used this reaction with recyclable palladium-complexed dendrimers on silica to synthesize 1,4-oxazepines. Remarkably, starting from iodinated arylamine 121, as a substrate for the intramolecular carbonylation, quantitative conversion to the pentacyclic heterocycle 122, containing two oxazepine rings, was achieved (Equation 11) <2005JA14776>. 

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