Asymmetric synthesis of planar chiral (Arene) tricarbonylchromium complexes via enantioselective deprotonation by conformationally constrained chiral lithium-amide bases

摘要

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, [alpha](D)(20), is found to be positive. except for the trimethylstannyl derivative 18b. This is interpreted in terms of a reversed conformation of the aldehyde group. [References: 80]