Ferrocenylphosphine chiral

The gold(I) complex of a chiral ferrocenylphosphine complex promotes asymmetric aldol reactions of a-isocyanocarboxylates to form chiral oxazolines in high diastereo- and enantio-selectivities (Scheme 52).225,226 In these reactions, the analogous silver(I) ferrocenylphosphine complex also works well. 

This alkylation reaction can be applied to intramolecular alkylation affording cyclic products, as shown in Equations (19)-(21). The reaction of 2-vinylpyridines with 1,5- or 1,6-dienes results in the formation of five- or six-membered carbocycles with good efficiency.20,20a,20b In addition to pyridine functionality, oxozole and imidazole rings can be applied to this intramolecular cyclization. When the reaction is conducted in the presence of a monodentate chiral ferrocenylphosphine and [RhCl(coe)2]2, enantiomerically enriched carbocycles are obtained. A similar type of intramolecular cyclization is applied to TV-heterocycles. The microwave irradiation strongly... 

In the asymmetric hydrosilylation of 1,3-cyclohexadiene 38 (Scheme 10, Table 4), catalyzed by chiral ferrocenylphosphines 5 and 40, the enantioselectivity is higher with phenyldifluorosilane than that with trichlorosilane or methyldichlorosilane (entries 1—4). The reaction of 38 with phenyldifluorosilane in the presence of a palladium catalyst coordinated with ferrocenylphosphine 40b gave allylsilane (A)-39c with 77% ee.58,59 The use of (j3-N-sulfonylaminoalkyl (phosphine 35a for the reaction of 38 with methyldichlorosilane exhibited the same level of asymmetric induction (entries 5-6).53 In this asymmetric hydrosilylation, combination of trichlorosilane and... 

Asymmetric Aldol Reactions with a Chiral Ferrocenylphosphine-Gold( I) Complex... 

TABLE 6-1. Asymmetric Hydrogenation of Trisubstituted Acrylic Acids Catalyzed by Chiral Ferrocenylphosphine-Rhodium Complexes... 

Asymmetric Synthesis Catalyzed by Chiral Ferrocenylphosphine Complex... 

Asymmetric aldol reaction. In the presence of a gold(I) complex (1) and a chiral ferrocenylphosphine (2), various aldehydes react with methyl isocyanoacetate... 

Further investigations are needed to establish, whether this approach is really useful to obtain chiral allylsilanes 2, which are synthetically quite interesting intermediates. They are available otherwise only by asymmetric cross-coupling of silyl alkyl Grignard reagents with bromoethylenes in the presence of a chiral ferrocenylphosphine-palladium catalyst54. 

An asymmetric preparation of alkenylcyclopropanes has also been realized by the use of palladium(O) complexes carrying chiral ferrocenylphosphine ligands (equation 22)38. The requisite rt-allyl palladium intermediates can also be generated from allene and meth-ylenecyclopropane derivatives, 1839 and 1940, in the presence of palladium(O) complex and alkenyl or aryl halide (equations 23 and 24). The cobalt complexes, 20, similarly afford the corresponding alkenylcyclopropanes upon exposure to LDA (equation 25)41. 

In 1986 Ito, Sawamura, and Hayashi [4] reported that gold(I) complexes prepared from cationic gold complex 1 and chiral ferrocenylphosphine ligands (2) bearing a tertiary amino group at the terminal position of a pendant chain are effective catalysts for asymmetric aldol reaction of... 

Among chiral phosphine ligands used for the nickel- or palladium-catalyzed asymmetric cross-coupling, a series of the ferrocenylphosphines has shown a great success in terms of enantioselectivity and a variety of modified chiral ferrocenylphosphines has been applied to the reaction (10-16). The first example of asymmetric cross-coupling catalyzed by... 

Figure 8F.2. Chiral ferrocenylphosphines for asymmetric cross-coupling.

Asymmetric hydrosilylation of styrene with HSiCl3 catalyzed by a palladium complex of a chiral ferrocenylphosphine attached to cross-linked polystyrene support at 70 °C gives PhMeC HSiCl3 in quantitative yield with only 15.2% ee65. 

Most catalysts that have been developed for asymmetric catalysis contain chiral C2-symmetric bisphosphines.7 The development of chiral ferrocenylphosphines ventures away from this conventional wisdom. Chirality in this class of ligands can result from planar chirality due to 1,2-unsymmetrically ferrocene structure as well as from various chiral substituents. Two classes of ferrocenylbisphosphines exist two phosphino groups substituted at the l,l -position about the ferrocene backbone (51) and both phosphino groups contained within a single cyclopentadienyl (Cp) ring of ferrocene (4).9... 

Illuminated by these promising results, several new chiral ferrocenylphosphine ligands were thus prepared. ° ° The enantioselectivity of the bicycloannulation... 

He, X. C. Wang, B. Yu, G. L. Bai, D. L. Studies on the asymmetric synthesis of huperzine A. Part 2 highly enantioselective palladium-catalyzed bicycloannulation of the beta-keto-ester using new chiral ferrocenylphosphine ligands. Tetrahedron-Asymmetry, 2001, 12(23) 3213-3216. 

A large fraction of the catalysts investigated for this purpose is on the basis of palladium or nickel complexes with chiral ferrocenylphosphine derivatives. This interest was spurred by the early work of Hayashi and Kumada who achieved the asymmetric coupling depicted in equation (5) (R = H) in 68% ee using phosphine (3) to provide chirality at the catalytic center. More recently, Knochel synthesized bisphosphine derivative (4) (R = Ph) which gave results similar to (3) when vinyl bromide was the substrate (equation 5, R = H, 63% ee). However, when the reaction was performed with /3-bromostyrene (R = Ph), the enantioselectivity see Enantioselectivity) increased to 93%. 

Kumada et al. have examined a number of chiral ferrocenylphosphines as ligands for asymmetric reactions catalyzed by transition metals. They are of interest because they contain a planar element of chirality as well as an asymmetric carbon atom. They were first used in combination with rhodium catalysts for asymmetric hydrosilylation of ketones with di- and trialkylsilanes in moderate optical yields (5-50%). High stereoselectivity was observed in the hydrogenation of a-acetamidoacrylic acids (equation 1) with rhodium catalysts and ferrocenylphosphines. ... 

Stereoselective hydrosilylation of alkadienes is also brought about using chiral ferrocenylphosphine-palladium complexes15. 

Table 3. Diastereo- and enantioselective aldol reaction of methyl isocyanoacetate (27) with tildehydes catalyzed by chiral ferrocenylphosphine 86c gold(I) complex.

The chiral ferrocenylphosphine.gold(I)-catalyzed aldol reaction of a-alkyl a-isocya-nocarboxylates 92 with paraformaldehyde gives optically active 4-alkyl-2-oxazoline-4-carboxylates 93 with moderate to good enantioselectivity [46], The absolute configuration (S) of the product indicates that the reaction occurs selectively at the si face of the enolate as illustrated in Fig. 2. These oxazolines 93 can be converted into a-alkyl-serine derivatives 94 (Sch. 24). 

Ito and coworkers found that chiral ferrocenylphosphine-silver(I) complexes also catalyze the asymmetric aldol reaction of isocyanoacetate with aldehydes (Sch. 26) [51]. It is essential to keep the isocyanoacetate at a low concentration to obtain a product with high optical purity. They performed IR studies on the structures of gold(I) and silver(I) complexes with chiral ferrocenylphosphine 86a in the presence of methyl isocyanoacetate (27) and found significant differences between the iso-cyanoacetate-to-metal coordination numbers of these metal complexes (Sch. 27). The gold(I) complex has the tricoordinated structure 100, which results in high ee, whereas for the silver(I) complex there is an equilibrium between the tricoordinated structure 101 and the tetracoordinated structure 102, which results in low enantioselectivity. Slow addition of isocyanoacetate 27 to a solution of the silver(I) catalyst and aldehyde is effective in reducing the undesirable tetracoordinated species and results in high enantioselectivity. 

Soloshonok and Hayashi applied chiral ferrocenylphosphine-gold(I) complexes to asymmetric aldol-type reactions of fluorinated benzaldehydes with methyl isocyano-acetate (27) and A, A/-dimethyl-a-isocyanoacetamide (95). It is noteworthy that successive substitution of hydrogen atoms by fluorine in the phenyl ring of benzaldehyde causes gradual increase of both the cis selectivity and the ee of cw-oxazolines [53]. 

Asymmetric Catalysis with Chiral Ferrocenylphosphine Ligands... 

The main purpose of this article is to survey the asymmetric reactions catalyzed by chiral ferrocenylphosphine-metal complexes, focusing attention on the design of the chiral ligand. 

Chiral ferrocenylphosphines were first prepared by Hayashi and Kumada in 1974 [7], The asymmetric ortho-lithiation of optically resolved iV,iV-dimethyl-l-ferrocenyl-ethylamine 1 with butyllithium reported by Ugi and coworkers [8] (see Chapter 4) was conveniently used for their preparation. The addition of diphenylchloro-phosphine to the ortho-lithiated ferrocene 2 generated from (/ )- gave R)-N,N-dimethyl-l-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine ((/ )-(S)-PPFA 3a) in 60 — 70% yield (Scheme 2-1) [9], The first R) designates the carbon central chirality... 

Structure of Chiral Ferrocenylphosphines and their Transition-Metal Complexes... 

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