Carbonylative ruthenium-catalyzed

The plausible mechanism of this ruthenium-catalyzed isomerization of allylic alcohols is shown in Scheme 15. This reaction proceeds via dehydrogenation of an allylic alcohol to the corresponding unsaturated carbonyl compound followed by re-addition of the metal hydride to the double bond. This mechanism involves dissociation of one phosphine ligand. Indeed, the replacement of two triphenylphosphines by various bidentate ligands led to a significant decrease in the reactivity.37... 

Ruthenium-catalyzed carbonylations of a variety of heterocycles have been disclosed. With benzimidazole derivatives, the regioselectivity changes upon introduction of a C(2) substituent (Equations (107) and (108)).100... 

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

An allenylaldehyde can be transformed efficiently into an a-methylene-y-butyro-lactone by a ruthenium-catalyzed carbonylative cycloaddition process (Scheme 16.34) [37]. The reaction mechanism may involve a metallacyclopentene, which undergoes insertion of CO and reductive elimination leading to the product. 

More recently, using the cyclometallated iridium C,(7-benzoate derived from allyl acetate, 4-methoxy-3-nitrobenzoic acid and BIPHEP, catalytic carbonyl crotylation employing 1,3-butadiene from the aldehyde, or alcohol oxidation was achieved under transfer hydrogenation conditions [274]. Carbonyl addition occurs with roughly equal facility from the alcohol or aldehyde oxidation level. However, products are obtained as diastereomeric mixtures. Stereoselective variants of these processes are under development. It should be noted that under the conditions of ruthenium-catalyzed transfer hydrogenation, conjugated dienes, including butadiene, couple to alcohols or aldehydes to provide either products of carbonyl crotylation or p,y-enones (Scheme 16) [275, 276]. 

Lee s group has also reported ruthenium-catalyzed carbonylative cyclization of 1,6-diynes. The noteworthy aspect of this cyclization is the unprecedented anti nucleophile attack on a 7i-alkyne complex bearing a ruthenium vinylidene functionality. A catalytic system based on [Ru(p-cymene)Cl2]2/P(4-F-C6H4)3/DMAP was active for the cyclization of 1,6-diyne 103 and benzoic acid in dioxane at 65 °Cto afford cydohexenylidene enol ester 104a in 74% yield after 24h [34]. Additional examples are shown in Scheme 6.35. 

Comparable lactones 19 can be synthesized from allenyl alcohols 18 by a ruthenium-catalyzed carbonylative cyclization [19] and an extension of this procedure to the synthesis of lactames 21 has also been reported [20]. 

Ruthenium-catalyzed ortho-Activation of Carbonyl-substituted Arenes... 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

The ruthenium-catalyzed [2+2+2] cycloaddition of 1,6-diynes was performed with an electron-deficient carbonyl double bond, activated with two electron-withdrawing groups, to produce conjugated dienones via electrocyclic ring opening of the expected cycloadduct [101] (Eq. 77). 

Ruthenium complexes are also suitable catalysts for carbonylation reactions of a variety of substrates. Indeed, when a reaction leads to C-Ru or het-eroatom-Ru bond formation in the presence of carbon monoxide, CO insertion can take place at the coordinatively unsaturated ruthenium center, leading to linear ketones or lactones. Thus, ruthenium-catalyzed carbonylative cyclization was involved in the synthesis of cyclopentenones by reaction of allylic carbonates with alkenes in the presence of carbon monoxide [124] (Eq. 93). 

Recently, the transition-metal-catalyzed addition of active methylene C-H bonds to electron-deficient olefins having a carbonyl, a nitrile, or a sulfonyl group has been extensively studied by several research groups. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers [88]. Another topic of recent interest is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. In this section, the ruthenium-catalyzed addition of C-H bonds in active methylene compounds to carbonyl groups and C-C multiple bonds is described. 

Abstract Ruthenium-catalyzed carbonylation reactions are described. The purpose of this chapter is to show how ruthenium complexes as catalysts are important in the recent development of carbonylation reactions. This review does not present a complete, historical coverage of ruthenium-catalyzed carbonylation reactions,but presents the most significant developments of the last 10 years. The emphasis is on novel and synthetic transformations of genuine value to organic chemists. Especially, this review will focus on carbonylative cycloadditions and carbonylation of C-H bonds. The review is generally organized according to the nature of the reaction. 

Ruthenium is not an effective catalyst in many catalytic reactions however, it is becoming one of the most novel and promising metals with respect to organic synthesis. The recent discovery of C-H bond activation reactions [38] and alkene metathesis reactions [54] catalyzed by ruthenium complexes has had a significant impact on organic chemistry as well as other chemically related fields, such as natural product synthesis, polymer science, and material sciences. Similarly, carbonylation reactions catalyzed by ruthenium complexes have also been extensively developed. Compared with other transition-metal-catalyzed carbonylation reactions, ruthenium complexes are known to catalyze a few carbonylation reactions, such as hydroformylation or the reductive carbonylation of nitro compounds. In the last 10 years, a number of new carbonylation reactions have been discovered, as described in this chapter. We ex-... 

Ruthenium carbonyl complexes have been shown to catalyze a number of car-bonylation processes. The ruthenium-catalyzed intramolecular Pauson-Khand reaction was found to proceed in the presence of Ru3(CO)12 (Eq. 105) [165,166]. The reaction is a valuable tool for selective organic synthesis. 

Scheme 7. Suggested mechanism for the ruthenium-catalyzed carbonylations of alcohols.

Although a whole series of carbonyl complexes of other transition metals (Fe, Mo, W, Ni) could only be used in stoichiometric Pauson-Khand reactions [11], two Japanese laboratories have since independently reported efficient ruthenium-catalyzed (intramolecular) reactions. The desired cy-clopentenones are formed in good to excellent yields in dimethylacetamide [12] or dioxane [13] in the presence of 2 mol% of [Ru3(CO),2] at 140-160 °C and 10-13 atm CO pressure. 

Ruthenium-catalyzed carbonylations of allylic compounds [62] were described in Chapter 11. Here, ruthenium-catalyzed carbonylative cyclization of allylic carbonates with alkenes, not alkynes, which offers a new route to cyclopentenones is revealed [63]. Treatment of allyl methyl carbonate with 2-norbornene in the presence of 2.5 mol% [RuCl2(CO)3]2 and 10 mol% Et3N in THE at 120°C for 5 h under 3 atm of carbon monoxide gave the corresponding cyclopentenone, exo-4-methyltri-cyclo[5.2.1.0 ]dec-4-en-3-one, in 80% yield with high stereoselectivity exo 100%) (Eq. 5.37). 

An example of ruthenium-catalyzed photo-induced C-H bond activation and successive carbonylation is the formation of benzaldehyde in the reaction of benzene and CO (800 torr) under UV irradiation (200 W, Hg-Xe) in the presence of RuCl-(CO)(NO)(PPh3)2 (Eq. 11.34) [75]. 

---