Asymmetric Carbonylation Reactions

Asymmetric Carbonylation Reactions.—Hydrofonnylation of Cgv alkenes [e.g. (Z)-MeCHCHMe] with [RhH(CO)(PPhs)3] + (-)-diop has been reported to yield a single aldehyde (3.8— 27% e.e.). J Cl2 (-)-diop ]-SnCl2 catalyses the hydrofonnylation of CH2=C(Ph)R (R = Me or Et). In contrast to a previous study, it is also reported that hydrofonnylation of but-l-ene, m-, or trans-but-2-ene with this catalyst gives different optical yields of 2-methylbutanal and therefore asymmetric induction takes place before the formation of metal-alkyl intermediates. [PdCl2(PhCN)2],L catalyses reaction (7) optical yields of 

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Abstract The use of Co building block in presence of water or an alcohol to functionalise alkenes by hydroxycarbonylation or alkoxycarbonylation reactions is reviewed in this chapter. The hydroxyl groups can be present in the substrate itself so cascade reactions can occur. Palladium precursors are largely involved in these reactions and this analysis of the literature focuses on the mechanisms involving Pd(0), Pd(H)(X)L2, PdX2 and an oxidant like CuCl systems. Introduction of chiral L or L2 ligands or even the presence of chiral carbon atoms in the substrate lead to asymmetric carbonylation reactions. 

Two approaches to asymmetric carbonylation reactions have met with some success. In the carbonylation reactions of a-methylbenzyl bromide under phase transfer catalysis, the... 

Despite these promising results, only a few articles have been reported so far on this asymmetric carbonylation reaction. 

Of course, the most practical and synthetically elegant approach to the asymmetric Darzens reaction would be to use a sub-stoichiometric amount of a chiral catalyst. The most notable approach has been the use of chiral phase-transfer catalysts. By rendering the intermediate etiolate 86 (Scheme 1.24) soluble in the reaction solvent, the phase-transfer catalyst can effectively provide the enolate with a chiral environment in which to react with carbonyl compounds. 

In 2000, these authors also developed a very efficient diphosphine-bithiophene ligand, tetraMe-BITIOP, which is depicted in Scheme 8.29. The ruthenium complex of this electron-rich diphosphine was used as the catalyst in asymmetric hydrogenation reactions of prostereogenic carbonyl functions of a-... 

Yang12 has effected an intramolecular asymmetric carbonyl-ene reaction between an alkene and an a-keto ester. Reaction optimization studies were performed by changing the Lewis acid, solvent, and chiral ligand. Ligand-accelerated catalysis was observed for Sc(OTf)3, Cu(OTf)2, and Zn(OTf)2 (Equation (6)). The resulting optically active m-l-hydroxyl-2-allyl esters provide an entry into multiple natural products. 

Jacobsen and co-workers14 have shown that a tridentate Schiff base chromium complex 13 catalyzed an asymmetric carbonyl-ene reaction between a variety of aryl aldehydes (14, Equation (8)) and 2-methoxy propene 15 or 2-trimethylsiloxypropene. The highest yields were afforded when the aryl ring was substituted with an electron-withdrawing group however, the substituent did not seem to affect the enantioselectivity. 

Cationic cobalt(m) complexes have successfully been applied to the asymmetric carbonyl-ene reaction.15 The yield and enantioselectivity were dependent, to a large extent, upon the counterion, with SbF6- giving the best results (16, Equation (9)). The conditions were general for a variety of alkenes, but only glyoxaldehydes were used as the carbonyl component. 

Mikami and co-workers16-19 have done extensive work for developing catalysts for the asymmetric carbonyl-ene reaction. Excellent enantioselectivites are accessible with the binol-titanium catalyst 17 (Equation (10)) for the condensation of 2-methyl butadiene (R1 = vinyl) and glyoxalates (binol = l,T-binaphthalene-2,2 -diol).16 The products were further manipulated toward the total synthesis of (i )-(-)-ipsdienol. The oxo-titanium species 18 also provides excellent enantioselectivity in the coupling of a-methyl styrene with methyl glyoxalate.17 Reasonable yields and good enantioselectivites are also obtained when the catalyst 19 is formed in situ from titanium isopropoxide and the binol and biphenol derivatives.18... 

The carbonyl group in a ketone or aldehyde is an extremely versatile vehicle for the introduction of functionality. Reaction can occur at the carbonyl carbon atom using the carbonyl group as an electrophile or through enolate formation upon removal of an acidic proton at the adjacent carbon atom. Although the carbonyl group is an integral part of the nucleophile, a carbonyl compound can also be considered as an enophile when involved in an asymmetric carbonyl-ene reaction or dienophile in an asymmetric hetero Diels-Alder reaction. These two types of reaction are discussed in the next three chapters. 

The prime functional group for constructing C-C bonds may be the carbonyl group, functioning as either an electrophile (Eq. 1) or via its enolate derivative as a nucleophile (Eqs. 2 and 3). The objective of this chapter is to survey the issue of asymmetric inductions involving the reaction between enolates derived from carbonyl compounds and alkyl halide electrophiles. The addition of a nucleophile toward a carbonyl group, especially in the catalytic manner, is presented as well. Asymmetric aldol reactions and the related allylation reactions (Eq. 3) are the topics of Chapter 3. Reduction of carbonyl groups is discussed in Chapter 4. 

This asymmetric catalytic reaction has found wide application in converting functionalized ketones to the corresponding secondary alcohols with high ee. A general illustration is given in Scheme 6-32. Five- to seven-membered chelate complexes, formed by the interaction of the Ru atom with carbonyl oxygen and a heteroatom X, Y, or Z may be the key intermediates that cause the high enantioselectivity in the reaction.67... 

A more versatile method to use organic polymers in enantioselective catalysis is to employ these as catalytic supports for chiral ligands. This approach has been primarily applied in reactions as asymmetric hydrogenation of prochiral alkenes, asymmetric reduction of ketone and 1,2-additions to carbonyl groups. Later work has included additional studies dealing with Lewis acid-catalyzed Diels-Alder reactions, asymmetric epoxidation, and asymmetric dihydroxylation reactions. Enantioselective catalysis using polymer-supported catalysts is covered rather recently in a review by Bergbreiter [257],... 

Abstract The transition metal mediated conversion of alkynes, alkenes, and carbon monoxide in a formal [2 + 2+1] cycloaddition process, commonly known as the Pauson-Khand reaction (PKR), is an elegant method for the construction of cyclopentenone scaffolds. During the last decade, significant improvements have been achieved in this area. For instance, catalytic PKR variants are nowadays possible with different metal sources. In addition, new asymmetric approaches were established and the reaction has been applied as a key step in various total syntheses. Recent work has also focused on the development of CO-free conditions, incorporating transfer carbonylation reactions. This review attempts to cover the most important developments in this area. 

The range of the asymmetric epoxidation reaction may be extended still further to include dienes (Entries 7,12,17) and even tetraenes (Entry 26). It is of interest to note that only double bonds adjacent to the carbonyl function are epoxidised and any remaining double bonds are left untouched (Entry 26). This selective reactivity allows for further elaboration of unreacted alkene units at a later stage, (see Sect. 5). Enediones (Entries 21-23) and unsatuxated keto esters (Entries 24 and 25) can also be oxidised in good yields and good to excellent stereoselectivity using polyamino acids. 

The Ti(0 Pr)2Cl2/D-DIPT poison has also been used for the Ti(0 Pr)2Cl2/ BINOL-catalyzed asymmetric carbonyl-ene reaction with chloral (Scheme 8.8). With the Ti(0 Pr)4/D-DIPT poison in a 1 3 ratio, both the regioselectivity and the enantioselectivity of the ene product are improved. 

The poor diastereoselectivity of the reactions of chiral aldehydes and achiral allylboronates appeared to be a problem that could be solved by recourse to the strategy of double asymmetric synthesis.f Our studies thus moved into this new arena of asymmetric synthesis, our objective being the development of a chiral allylboron reagent capable of controlling the stereochemical outcome of reactions with chiral aldehydes independent of any diastereofacial preference on the part of the carbonyl reaction partner. 

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

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