Cycloadditions carbonylative

IH-Azepine, 1-methoxy carbonyl-cycloaddition reactions, 7, 522 with nitrosobenzene, 7, 520 tricarbonyliron complex acylation, 7, 512-513 conformation, 7, 494 tricarbonylruthenium complex cycloaddition reactions, 7, 520 1 H-Azepine, l-methoxycarbonyl-6,7-dihydro-synthesis, 7, 507... 

TMM cycloadditions to cyclic and conjugated ketones have also been reported (Scheme 2.22) [31]. The steric nature of the substrate does play a critical role in determining product formation. Thus the cyclic ketone (73) produced 55% yield of the tetrahydrofuran, but no cycloadduct could be obtained from the cyclic ketone (74). The enone (75) gave only carbonyl cycloaddition, whereas enone (76) yielded only olefin adduct. Interestingly, both modes of cycloaddition were observed with the enone (77). The ynone (78) also cycloadds exclusively at the carbonyl function [34]. 

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. 

Figure 2 Photochemical hydrogen transfer and carbonyl cycloaddition.

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. 

Keywords Carbonylation Ruthenium Carbon monoxide Carbonylative cycloaddition C-H bond activation... 

Metal complexes enable one to employ molecules that are thermally unreactive toward cycloadditions by taking advantage of their ability to be activated through complexation. Most of the molecules activated by transition-metal complexes involve C-C unsaturated bonds such as alkynes, alkenes, 1,3-dienes, allenes, and cyclopropanes. In contrast, carbonyl functionalities such as aldehydes, ketones, esters, and imines seldom participate in transition-metal-catalyzed carbonylative cycloaddition reactions. Recently, such a transformation was reported via the use of ruthenium complexes. 

Among the carbonylative cycloaddition reactions, the Pauson-Khand (P-K) reaction, in which an alkyne, an alkene, and carbon monoxide are condensed in a formal [2+2+1] cycloaddition to form cyclopentenones, has attracted considerable attention [3]. Significant progress in this reaction has been made in this decade. In the past, a stoichiometric amount of Co2(CO)8 was used as the source of CO. Various additive promoters, such as amines, amine N-oxides, phosphanes, ethers, and sulfides, have been developed thus far for a stoichiometric P-K reaction to proceed under milder reaction conditions. Other transition-metal carbonyl complexes, such as Fe(CO)4(acetone), W(CO)5(tetrahydrofuran), W(CO)5F, Cp2Mo2(CO)4, where Cp is cyclopentadienyl, and Mo(CO)6, are also used as the source of CO in place of Co2(CO)8. There has been significant interest in developing catalytic variants of the P-K reaction. Rautenstrauch et al. [4] reported the first catalytic P-K reaction in which alkenes are limited to reactive alkenes, such as ethylene and norbornene. Since 1994 when Jeong et al. [5] reported the first catalytic intramolecular P-K reaction, most attention has been focused on the modification of the cobalt catalytic system [3]. Recently, other transition-metal complexes, such as Ti [6], Rh [7], and Ir complexes [8], have been found to be active for intramolecular P-K reactions. 

An ester carbonyl group is known to be generally less reactive than an aldehyde or a ketone carbonyl group. As a result, cycloaddition reactions of esters under thermal conditions are very rare. In a unique case, Chatani et al. [23] found that an ester functionality also participates in the carbonylative cycloaddition reaction of a-ketolactones (Eq. 11). The presence of a bulky group next to the keto carbonyl group is required for this selective reaction. 

An important discovery in the area of carbonyl cycloadditions is that highly oxygenated 1,3-dienes are excellent 4ir components. These reactions occur at low temperatures with a wide range of aldehydes provided Lewis acid catalysts are used. " " This general type of reaction is shown by the example in equation (81). It was also found by Danishefsky and coworkers that lanthanide shift reagents are elective catalysts for the cycloaddition.An example of one of these cycloadditions is outlined in equation (82). 2 <>... 

Studies on the control of product selectivity and regioselectivity in tetracarbonylnickel-promot-ed carbonylative cycloaddition of allylic halides and acetylenes reveal an influence of the solvent and the substitution pattern in both the acetylenes and the allylic halides. Thus, by appropriate choice of the reaction conditions, cyclopentenone derivatives can be obtained in satisfactory yield46,419,12°. 

Carbonylative cycloaddition of allyl bromides and acetylenes in methanol in the presence of nickel tetracarbonyl results in the formation of cyclopentenones. For instance, 3-bromocyclopentene and methyl but-2-ynoate afford the diester 493, the halogen atom being replaced by the methoxycarbonyl group. Nickel tetracarbonyl also catalyses the reaction of l-(bromomethyl) cycloalkenes 494 of ring size 5-8 with methyl but-2-ynoate in methanol to yield the spiro-compounds 495 (equation 54). ... 

Metal-Catalyzed Carbonylative Cycloaddition Reactions of Benzyne. 142... 

Although nickel-catalyzed carbonylative Pauson-Khand cycloadditions have not been broadly developed, related doubly carbonylative cycloadditions involving allyl halides have been demonstrated as an entry to functionalized cyclopentenones. In recent catalytic versions, iron powder was used as the terminal reductant and dehalogenating agent (Scheme 3-38). [Caution Ni(CO)4, which could potentially be liberated in this reaction, is a highly toxic gas.]... 

Scheme 1.2 Ruthenium-catalyzed intermolecular carbonylative cycloaddition reaction.

Even though Ni(CO)4 is called liquid death, this nickel catalyst has been applied in carbonylation reactions [52]. The group of Ricart reported a nickel-catalyzed carbonylative cycloaddition of alkynes and aUyl hahdes to cyclopentanes. The desired products were obtained in high yields and with controlled stereoselectivity. Iron was used as a reductant. An extension of the reaction to new substrates led to the conclusion that, although the steric and electronic effects of the alkyne substituents are generally irrelevant in relation to the adducts and their yields, those of the allylic counterpart may have a significant influence on the outcome of the reaction. However, the presence of the amine moiety in the alkyne completely inhibited the reaction. The feasibility of a multicentered reaction was verified with a triacetylene, in which up to 12 bonds were created simultaneously and in good yield (Scheme 1.30). 

We tried to take advantage of the mentioned activation in other type of reactions[5]. Since the Co mediated carbonylative cycloaddition of alkynes and olefins (Pauson-Khand reaction) is under extensive study, we advanced that the mentioned triple bonallow reaction completion under milder temperatures than those usually required. While no reaction was found... 

At the present, our studies with alkynylcarbene complexes of Cr and W suggest that their cycloadditions with electron-rich olefins follow, mainly, a concerted [2+2] pathway by activation of the triple bond[6], whereas, the intramolecular Co-induced carbonylative cycloaddition of the corresponding allylamino complexes seems to be facilitated by the alternative influence of the metal on the heteroatom side. A strict control of the stereochemistry in these reactions has been observed making these complexes valuable auxiliaries in organic synthesis. Efforts to broaden the scope of application are under way. 

Presence of an electron-rich substituent, PMP, on the nitrogen atom retards the reaction to some extent. The carbonylative cycloaddition of imines derived from both aliphatic and aromatic amines affords cw-/S-lactams with high stereoselectivity in spite of their susceptibihty to epimerization. 

The imines derived from vicinal dicarbonyl substances afford cis-lactams (Scheme 2), whereas the imines prepared from aryl and alkenyl aldehydes yield trans-lactams (Schemes 3 and 4). The different basis for the stereoselection in the carbonylative cycloaddition from that of the usual base-induced process is worthy of anphasis. The mechanism of this carbonylative formal [2 + 2] cycloaddition is discussed in comparison with the results of the base-induced ketene-imine cycloaddition,... 

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