Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium-Amide Bases

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Enantioselective lithiation/electrophile addition reactions with eight chiral Li-amide bases, 1 – 8, and five [Cr(arene)(CO)3] complexes, 9 – 13, were investigated. Restriction of conformational freedom in the chiral Li-amide base Li-1, in general, did not result in an increase in asymmetric induction. A new route to enantiomerically enriched (75 – 92%) planar chiral ortho-substituted benzaldehyde complexes via enantioselective lithiation of benzaldimine complexes 16 and 17 is reported. Within the (1S)-enantiomer series of o-substituted benzaldehyde complexes 18a – d, the sign of the specific rotation, [α], is found to be positive, except for the trimethylstannyl derivative 18b. This is interpreted in terms of a reversed conformation of the aldehyde group.