Biaryl arene chromium tricarbonyl

This class of amides has been made enantio-selectively - albeit in low yield and low ee -by an ortholithiation reaction (Scheme 10). More successful is Uemura s demonstration [19] that the arene-chromium tricarbonyl complex chemistry that works with atroposelectivc biaryl couplings is also successful with atropose-lective amide-forming reactions (Scheme 11). 

Biaryls with axial chirality are potentially important as chiral ligands for asymmetrical reactions and also as intermediates for synthesizing biologically active natural biaryl compounds, for example, michellamine in Eq. 66. (ii -Disubstituted arene)chromium tricarbonyl complexes exist in two enantiomeric forms based on planar chirality. Biaryl coupling provides a new approach to synthesizing both optically pure atropisom-ers starting from a single chiral arene chromium complex (Eq. 75). ... 

The control of stereochemistry with chromium carbine complexes has been reviewed. The DBR can create a new stereocenter in three ways. First, the arene tricarbonyl chromium complex contains a plane of chriality, thus the complexes 35 and ent-35 are enantiomers when RL Ri and RS R2. Second, when phenyl substituents are included in the reactants the resulting biaryls can posess axial chirality if there is hindered rotation about the new aryl-aryl bond as in 36. Finally, all DBRs with differentially p-disubstitued alkenes give rise to cyclohexadienones 37 with a new stereocenter adjacent to the carbonyl. When Ri and R2 are not hydrogen, tautomerization cannot occur and the final product possesses a chiral center. 

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