Compounds symmetry-based design

Rh(II) carboxylates, especially Rh2(OAc)4> have emerged as the most generally effective catalysts for metal carbene transformations [7-10] and thus interest continues in the design and development of dirhodium(II) complexes that possess chiral51igands. They are structurally well-defined, with D2h symmetry [51] and axial coordination sites at which carbene formation occurs in reactions with diazo compounds. With chiral dirhodium(II) carboxylates the asymmetric center is located relatively far from the carbene center in the metal carbene intermediate. The first of these to be reported with applications to cyclopropanation reactions was developed by Brunner [52], who prepared 13 chiral dirhodium(II) tetrakis(car-boxylate) derivatives (16) from enantiomerically pure carboxylic acids RlR2R3CC OOH with substituents that were varied from H, Me, and Ph to OH, NHAc, and CF3. However, reactions performed between ethyl diazoacetate and styrene yielded cyclopropane products whose enantiopurities were less than 12% ee, a situation analogous to that encountered by Nozaki [2] in the first applications of chiral Schiff base-Cu(II) catalysts. 

Conclusion. The C2 symmetry of (R,R)- and (S,S)-1,2-diaminocyclohexane, readily available from the racemic compound by resolution, has served as a versatile chiral motif in the design of topologically unique stereodifferentiating reagents such as the phosphonamide anions described here. Several other applications of these reagents via anion chemistry, or simply based on the exploitation of other effects offered by their structures and heteroatom functionality, can be explored (catalytic processes, chiral ligands, etc.). The lYfY-disubstituted 1,2-diaminocyclohexane motif has also been remarkably versatile in other asymmetric processes such as the dihydroxylation of alkenes, and a variety of other C-C bond-forming reactions. ... 

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