Enol phosphinates, asymmetric

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands 63 Table 12 Asymmetric hydrogenation of enol phosphinates... 

Enantioselective transfer hydrogenation (from propan-2-ol) of some ketones catalysed by iridium(i) complexes with chiral Schifl-base ligands has been reported, giving product alcohol of up to 33% e.e. with propiophenone as substrate. Other new reductive routes to chiral secondary alcohols involve the asymmetric hydrogenation of enol phosphinates (21) catalysed by chiral ferrocenyl-rhodium... 

Ferraris et al.108 demonstrated an asymmetric Mannich-type reaction using chiral late-transition metal phosphine complexes as the catalyst. As shown in Scheme 3-59, the enantioselective addition of enol silyl ether to a-imino esters proceeds at —80°C, providing the product with moderate yield but very high enantioselectivity (over 99%). 

The asymmetric fluorination of enolates by means of chiral metal complexes has been reported with Selectfluor in the presence of a chiral Lewis acid derived from TADDOL (TiCl2/TADDOL), or with F-A-sulfonimide (NFSI) with palladium complexes and chiral phosphines. 

Acyliron complexes with central chirality at the metal are obtained by substitution of a carbon monoxide with a phosphine ligand. Kinetic resolution of the racemic acyliron complex can be achieved by aldol reaction with (1 R)-( I (-camphor (Scheme 1.14) [41], Along with the enantiopure (R, c)-acyliron complex, the (Spe)-acyliron-camphor adduct is formed, which on treatment with base (NaH or NaOMe) is converted to the initial (SFe)-acyliron complex. Enantiopure acyliron complexes represent excellent chiral auxiliaries, which by reaction of the acyliron enolates with electrophiles provide high asymmetric inductions due to the proximity of the chiral metal center. Finally, demetallation releases the enantiopure organic products. 

The peptidic phosphine ligands that had been introduced by Hoveyda and co-workers271 for enantioselective copper-catalyzed Michael additions (see Section 9.12.2.2.1) were also employed successfully in silver-catalyzed asymmetric Mannich reactions.3 Thus, the aryl-substituted imines 372 reacted with various silyl enol ethers in the presence of stoichiometric amounts of isopropanol, as well as catalytic amounts of silver acetate and ligand 373 to... 

Bergman and Heathcock have demonstrated fhat fhe Rh(I)-catalyzed aldol reaction, originally reported by Matsuda et al, [87], proceeds via Rh(l) enolates 25 and aldolates 26 (Scheme 10.25) [88]. This type of transition metal-catalyzed aldol reaction has been used for asymmetric synthesis using readily accessible chiral phosphines (vide infra). 

The Morita-Baylis-Hillman (MBH) reaction is an important 100% atom economic transformation that allows the formation in one step of a flexible allylic alcohol motif. Efforts in this field have been directed recently to the solution of two problems to enhance the generally sluggish reaction rate and to achieve asymmetric catalytic versions. Scheme 1.15 gives the catalytic cycle of the MBH reaction. The catalyst is a highly nucleophilic tertiary amine, generally DABCO, or a tertiary phosphine, which adds to the oc,P-unsaturated electrophile in a 1,4 fashion to deliver an enolate that, in turn, adds to the aldehyde. A critical step is the proton transfer from the enolizable position to the oxygen atom this process is catalysed by an alcohol that plays the role of a proton shuttle between the two positions. Water has also been reported to strongly speed up the reaction at a well-defined concentration. Moreover, the... 

Enolates, generated by Michael addition reactions of a,p-unsaturated esters or ketones, can add to aldehydes. If the Michael addition is carried out with a tertiary amine (or phosphine) then this is referred to as the Baylis-Hillman reaction. Typically, an amine such as l,4-diazabicyclo[2.2.2]octane (DABCO) is used. After the aldol reaction, the tertiary amine is eliminated and it can therefore be used as a catalyst (1.61). The reaction is somewhat slow (requiring several days), but rates may be enhanced with other amines such as quinuclidine or quinidine derivatives, the latter effecting asymmetric reaction with high levels of selectivity. ... 

Zhou SJ, Huang Z (2013) Chiral phosphines for palladium-catalyzed asymmetric alpha-arylation of ester enolates to produce tertiary stereocenters in high enantioselectivity. WO/2013/028132 http //ww w. google. com/patents/WO2013028132A1 cl=en... 

Carbon-carbon bond formation by using metal enolates as synthons in organic chemistry and the protonation, alkylation, arylation, and vinylation of enolates have been reviewed. " The stereoselective carbon-carbon formation of bond through Mannich reaction has been detailed according to the type of Mannich base produced. Phosphine-catalysed asymmetric additions of malonate esters to y-substituted allenoates and aUenamides have been reported. ... 

In analogy t 0 the Cu(II) complex systems, the silver(I) -catalyzed aldol reaction is also proposed to proceed smoothly through a Lewis acidic activation of carbonyl compounds. Since Ito and co-workers reported the first example of the asymmetric aldol reaction of tosylmethyl isocyanide and aldehydes in the presence of a chiral silver(I)-phosphine complex (99,100), the catalyst systems of sil-ver(I) and chiral phosphines have been applied successfully in the aldol reaction of tin enolates and aldehydes (101), Mukaiyama aldol reaction (102), and aldol reaction of alkenyl trichloroacetates and aldehydes (103). In the Ag(I)-disphosphine complex catalyzed aldol reaction, Momiyama and Yamamoto have also examined an aldol-type reaction of tin enolates and nitrosobenzene with different silver-phosphine complexes (Scheme 15). The catalytic activity and enantioselectivity of AgOTfi(f )-BINAP (2 1) complex that a metal center coordinated to one phosphine and triflate were relay on solvent effect dramatically (Scheme) (104). One catalyst system solves two problems for the synthesis of different O- and AT-nitroso aldol adducts under controlled conditions. 

The use of palladium(II) 7i-allyl complexes in organic chemistry has a rich history. These complexes were the first examples of a C-M bond to be used as an electrophile [1-3]. At the dawn of the era of asymmetric catalysis, the use of chiral phosphines in palladium-catalyzed allylic alkylation reactions provided key early successes in asymmetric C-C bond formation that were an important validation of the usefulness of the field [4]. No researchers were more important to these innovations than Prof. B.M. Trost and Prof. J. Tsuji [5-10]. While most of the early discoveries in this field provided access to tertiary (3°) stereocenters formed on a prochiral electrophile [Eq. (1)] (Scheme 1), our interest focused on making quaternary (4°) stereocenters on prochiral enolates [Eq. (2)]. Recently, we have described decarboxylative asymmetric allylic alkylation reactions involving prochiral enolates that provide access to enantioenriched ot-quatemary carbonyl compounds [11-13]. We found that a range of substrates (e.g., allyl enol carbonates,... 

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