Chiral metal complexes conjugate addition

Mikami and coworkers also reported the development of lanthanide bis(trif-luoromethanesulfonyl)amides (bistrifylamides) as a new type of asymmetric catalysts for the hetero-Diels-Alder reaction of Danishefsky s diene, wherein the significant effect of water as an additive is observed in increasing not only the enan-tioselectivity but also the chemical yield. Bistrifylamides can be used as effective bidentate Hgands to increase the Lewis acidity of their chiral metal complexes on account of the higher acidity of the conjugated acids than those of afiphatic and aromatic diols, which are commonly used as chiral bidentate hgands [33]. 

Two distinct chiral metal complexes operate cooperatively to catalyze a highly enantioselective conjugate addition of cyanide to unsaturated imides (Scheme 5). Under optimized conditions, the dual-catalyst system afforded distinctly superior results relative to the (salen)AlCl complex. 

Gothelf presents in Chapter 6 a comprehensive review of metal-catalyzed 1,3-di-polar cycloaddition reactions, with the focus on the properties of different chiral Lewis-acid complexes. The general properties of a chiral aqua complex are presented in the next chapter by Kanamasa, who focuses on 1,3-dipolar cycloaddition reactions of nitrones, nitronates, and diazo compounds. The use of this complex as a highly efficient catalyst for carbo-Diels-Alder reactions and conjugate additions is also described. 

The l ,J -DBFOX/Ph-transition metal aqua complex catalysts should be suitable for the further applications to conjugate addition reactions of carbon nucleophiles [90-92]. What we challenged is the double activation method as a new methodology of catalyzed asymmetric reactions. Therein donor and acceptor molecules are both activated by achiral Lewis amines and chiral Lewis acids, respectively the chiral Lewis acid catalysts used in this reaction are J ,J -DBFOX/Ph-transition metal aqua complexes. 

Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds, 18, 151 13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds, 12, 135 Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, I, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365... 

Chiral phosphine ligands are the chiral auxiliaries extensively studied for transition metal-catalyzed asymmetric reactions. Most of the ligands were originally designed for asymmetric hydrogenation, but they also worked well in the conjugate addition of organoboronic acids to electron-deficient alkenes.951,952 The rhodium(i) complexes of 496-503953-966 have been successfully utilized for these asymmetric reactions (Scheme 37). 

Various other examples of nickel-catalyzed asymmetric addition of organozinc compounds to enones have been reported using different chiral auxiliaries111-117. Complexes of other transition metals, such as rhodium118-119, lanthanum120, and titanium121, have also been found to promote asymmetric conjugate addition of enolates to a,/i-unsaturated ketones. 

This complex has several interesting characteristics (i) it is easy to prepare and handle, (ii) it is chiral-at-iron and can be resolved, and (iii) the protons a to the acyl group are acidic and the corresponding metal acyl enolate undergoes a variety of transformations including alkylations, aldol reactions, conjugate addition reactions and Diels-Alder reactions (Scheme 3.6). 

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