Pauson asymmetric

Asymmetric Pauson-Khand reaction in syntheses of heterocycles fused with five-member carbocyclic fragment 980PP121. 

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 asymmetric reactions discussed in this chapter may be divided into three different types of reaction, as (1) hydrometallation of olefins followed by the C—C bond formation, (2) two C C bond formations on a formally divalent carbon atom, and (3) nucleophilic addition of cyanide or isocyanide anion to a carbonyl or its analogs (Scheme 4.1). For reaction type 1, here described are hydrocarbonyla-tion represented by hydroformylation and hydrocyanation. As for type 2, Pauson-Khand reaction and olefin/CO copolymerization are mentioned. Several nucleophilic additions to aldehydes and imines (or iminiums) are described as type 3. 

In the 1990s, successful catalytic asymmetric intermolecular Pauson-Khand reac-... 

The asymmetric catalytic Pauson-Khand reaction met success in the late 1990s. Not only the conventional Co catalyst but also other metal complexes, such as Ti, Rh, and Ir, are applicable to the reaction. Asymmetric hydrocyanation of vinylar-enes is accomplished using Ni complex of chiral diphosphite. Further studies on the scope and limitation are expected. 

Jeong and coworkers have executed a desymmetrization of a dienyne by asymmetric Pauson-Khand-type reaction. Intriguingly, the use of a Rh catalyst resulted in preferential formation of one diastereomer, while a switch to the analogous Ir system provided the other diastereomer in excellent selectivity [Eq. (10.62)] the system has been shown to be tolerant of oxygen in the linker as well as modest substitution on the alkyne (Ph) ... 

Enantiomerically pure trans-2-phenylcyclohexanol, first used by Whitesell as a chiral auxiliary has become a popular reagent in a number of asymmetric transformations. Some recent applications include asymmetric azo-ene reactions, [4 + 2]-cycloaddition reactions, ketene-olefin [2 + 2]-reactions, enolate-imine cyclocondensations, Pauson-Khand reactions," palladium annulations and Reformatsky reactions. Despite its potential, use of this chiral auxiliary on a preparative scale is currently limited by its prohibitive cost. 

Scheme 1.3.28 Asymmetric synthesis of bicyclic amino acids via Pauson-Khand cycloaddition of vinyl sulfoximines.

One of the earliest enantioselective carbon-carbon bond-forming processes catalyzed by chiral transition-metal complexes is asymmetric cyclopropanation discussed in Chapter 5, which can proceed via face-selective carbometallation of carbene-metal complexes. Some other more recently developed enantioselective carbon-carbon bond forming reactions, such as Pd-catalyzed enantioselective alkene-CO copolymerization (Chapter 7) and Pd-catalyzed enantioselective alkene cyclization (Chapter 8.7), are thought to involve face-selective carbometallation of acy 1-Pd and carbon-Pd bonds, respectively (Scheme 4.4). Similarly, the asymmetric Pauson-Khand reaction catalyzed by chiral Co complexes most likely involves face-selective cyclic carbometallation of chiral alkyne-Co complexes (Chapter 8,7). 

Oxidative alkoxycarbonylation asymmetric carbonylation, 11, 467 catalyst development, 11, 467 mechanism, 11, 466 Oxidative amination, olefins, 10, 155 Oxidative cleavage, mechanisms, 1, 103 Oxidative promoters, in Pauson-Khand reaction with dicobalt octacarbonyl, 11, 337... 

Parasites, antimicrobials for, 12, 458 Pauson-Khand reaction allenic substrates, 11, 352 and allenynes, 10, 356-357 with aminocarbonylation, 11, 531 asymmetric catalysts, in desymmetrizations, 11, 357 catalytic... 

The cyclopentenone 277 and a small amount of the cyclopentanone 278 are obtained by the carbonylation (1 atm) of titanacycle 276, generated from 1,6-enyne 275 and 273 [120], However, this Pauson-Khand type reaction of the 1,6-enyne proceeds with a catalytic amount of Cp2Ti(CO)2. Furthermore, asymmetric... 

Asymmetric Pauson-Khand bicyclization.1 Efficient asymmetric Pauson-Khand bicyclizations of enynes are possible using (lS,2R)-( + )-phenylcyclohexanol (13, 244 14, 128-129) as the chiral auxiliary. Thus the (E)-enol ether (1) derived... 

Highly efficient asymmetric intermolecular Pauson-Khand reactions have been developed by using the chiral phosphine ligand (/ )-(+)-g yphos and N-methylmorpholine A-oxide as a promoter (see Section II,C).178... 

Considerable efforts have been made to develop asymmetrical variants of the classical Pauson-Khand reaction. Initial investigations have shown that compounds derived from cobalt complexes of type 1, in which a carbonyl ligand is replaced by a chiral phosphane (glyphos), react with high enantioselectivity [22], However, the procedure is too complex to be of preparative value. The concept of Kerr et al., who achieved significant enantioselectivities (max. 44 % ee) in intermolecular Pauson-Khand reactions by... 

Similarly, intramolecular Pauson-Khand reactions can be utilized for tetrahydrofuran synthesis, when the tethers are oxa substituted. Ligand effects on stereoselectivity in Rh(i)-catalyzed asymmetric Pauson-Khand-type reactions have been investigated and ee s of up to 92% have been achieved with the 2,2-bis(diphenyl-phosphanyl)-l,l-binaphthyl (BINAP) ligand and a Rh(i) precatalyst (Equation 91). However, it has to be noted that the ee is highly substrate dependent, and considerably lower in most other cases <2006S4053>. 

Asymmetric intermolecular Pauson Khand reactions have been reahzed using a number of chiral auxiliaries chelating to the metal and/or attached to the alkyne. One example using a camphor-derived hgand is seen in Scheme 253. Moderate asymmetric induction has been observed using chiral amine A-oxides as the promoter. For example, (-F)-indohzino[3,4-b]quinoline A-oxide gave up to 53% ee. 

Ingate, S. T. Marco-Contelles, J. The Asymmetric Pauson-Khand Reaction, Org. Prep. Proc. Inti. 1998, 30, 121-143. 

Buchwald, S. L., Hicks, F. A. Pauson-Khand type reactions. Comprehensive Asymmetric Catalysis /-///1999, 2, 491-510. 

Kellogg, R. M. Rhodium(l)-catalyzed asymmetric intramolecular Pauson-Khand-type reaction. Chemtracts 2000, 13, 708-710. 

Kennedy, A. R., Kerr, W. J., Lindsay, D. M., Scott, J. S., Watson, S. P. Stereochemical and mechanistic features of asymmetric Pauson-Khand processes. Perkin 1 2000,4366-4372. 

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