Chiral cinchona alkaloid catalysts

When nitrostyrenes and dimethylmalonate were reacted with a,p-un-saturated aldehydes in the presence of a combination of chiral diphenyl-prolinol triethylsilyl ether and a chiral cinchona alkaloid catalyst through a three-component reaction, Xu et al. showed that they afforded, according to a Michael-Michael-aldol domino reaction, the corresponding chiral functionalised cyclohexanes in moderate to good yields, good to excellent enantioselectivities of up to >99% ee, albeit moderate diastereoselectivities... 

Scheme 2.37 Four-component tandem Michael-aza-Henry-hemiaminalisation-dehydration reaction catatysed by a chiral diaiylprolinol trimethyl-silyl ether and a chiral cinchona alkaloid catalyst.

Pt/Al2C>3-cinchona alkaloid catalyst system is widely used for enantioselective hydrogenation of different prochiral substrates, such as a-ketoesters [1-2], a,p-diketones, etc. [3-5], It has been shown that in the enantioselective hydrogenation of ethyl pyruvate (Etpy) under certain reaction conditions (low cinchonidine concentration, using toluene as a solvent) achiral tertiary amines (ATAs triethylamine, quinuclidine (Q) and DABCO) as additives increase not only the reaction rate, but the enantioselectivity [6], This observation has been explained by a virtual increase of chiral modifier concentration as a result of the shift in cinchonidine monomer - dimer equilibrium by ATAs [7],... 

Chiral versions of PEG-bound PTCs have been prepared by the attachment of cinchona alkaloids. Catalysts 101 and 102 (Figure 10.9), related to non-cationic 77, were prepared starting from monomethylated PEG5000 and using spacers similar to that of 98 [216]. Both materials were tested as catalysts for the synthesis of the tert-butyl ester related to 94 and similar compounds, using the standard O Donnell-Corey-Lygo procedure. Under optimized conditions (DCM, solid CsOH, — 78 °C,... 

Using chiral cinchona alkaloid derived PT catalysts (but achiral phosphines ), new amino acid derivatives were obtained in enantiomeric ees up to 96% [92], (3) The unusual coupling of four molecules sketched above was accomplished in high yield with Pd(0)/bis(dibenzylideneacetone) as metal and NBu4Br as PT catalyst in aqueous NaOH/CH2Cl2 at room temperature. 

Collier P.J., Goulding T., Iggo J.A. and Whyman R. (1995) Studies of the Pt-cinchona alkaloid catalyst for enantioselective alpha-keto esters hydrogenation, in Jannes G. and Dubois V. (eds.). Chiral Reactions in Heterogeneous Catalysis, Plenum Press, N.Y. p. 105-110. 

General principles applied on the design of chiral cinchona alkaloid-based chiral ammonium salt PTC catalysts. 

Finally, a remarkable four-component tandem Michael-aza-Henry-hemi-aminalisation-dehydration tandem reaction was recently developed by Lin and co-workers on the basis of a dual organocatalysis involving a chiral diaryl prolinol trimethylsilyl ether and a chiral cinchona alkaloid." As shown in Scheme 2.37, the reaction began with the Michael addition of an aldehyde to a nitroalkene catalysed by the L-proline-derived catalyst, giving the corresponding intermediate aldehyde. The latter intermediate... 

Later, an enantioselective one-pot tandem Mannich-hydroamination reaction was reported by Liu and co-workers on the basis of a sequential organo- and gold catalysis.The proeess involved propargylated malonitrile and oxindole imine derivatives as substrates and employed a chiral cinchona alkaloid, such as a quinidine phenol derivative, to induce the enantioselective Mannich reaction and a gold catalyst, such as XPhosAuNTfa... 

An enantioselective organocatalytic cyclopropanation reaction via chiral ammonium ylides was also developed. The reaction operates under an 8 2 process of a-halocarbonyl compounds by means of cinchona alkaloid catalysts, allowing the... 

Corey et al investigated chiral Cinchona alkaloid-based ammonium salt (28) as a catalyst for the enantioselective Strecker reaction (Scheme 2.69) [131]. They proposed that the acid could be used to hold the aldehyde-derived part of an aldimine, which was activated by hydrogen bonding with the protonated quinuclidine moiety. 

A new class of chiral bifunctional cinchona-alkaloid catalyst with urea moiety at C5 has recently been reported by Connon and coworkers, and successfully applied in enantioselective nitroaldol reaction of nitromethane with aromatic... 

Lectka has developed a number of innovative strategies for the enantioselective transformation of ketenes by activation with chiral amines [27, 129). In the presence of cinchona alkaloid catalyst 237 and base, acid chloride 236 is converted into zwitterion 238 (Scheme 3.35). These intermediates behave effectively as chiral enolates and partake in electrophilic chlorination and bromination reactions [130-132]. Upon treatment with brominating agent 239, the depicted brominated ester 240 was obtained in 68% yield and 98% optical purity [131],... 

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