Asymmetric Reaction Utilizing Planar Chiral Arenes

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(eta6-Arene) chromium complexes exist in two enantiomeric forms based on planar chirality, when the arene ring is substituted with two different groups. We have investigated for an asymmetric synthesis utilizing planar chiral (arene) chromium complexes in this research project.At first, enantiomerically active planar chiral (arene) chromium complexes were prepared by following methods. Racemic (omicron-substituted benzylalcohol) Cr(CO)_3 complexes were kinetically resolved by lipase in the presence of isopropenyl acetate into enantiomerically active chromium complexes in high enantiomeric excesses. Tricarbonylchromium-complexed protected phenol or aniline derivative was lithiated at the enantiotopic ortho position with chiral lithium diamine followed by quenching with electrophiles to give optically active (di-substituted arene) chromium complexes.Cross-coupling of (2,6-disubstituted halobenzene) chromium with o-substituted phenylboronic acids in the presence of palladium catalyst gave … More diastereoselectivelly Cr(CO)_3-complexed biaryls with complementary axial chirality depending upon the ortho-substituents of arylboronic acids. Reaction of omicron-alkyl or omicron-hydroxymethyl-substituted phenylboronic acid with (arylhalide) chromium complexes gave biaryls in which the ortho substituents are in a syn-orientation to the tricarbonylchromium fragment. With omicron-formyl phenylboronic acid, diastereoisomeric anti-coupling products were stereoselectively obtained. The kinetically controlled cross-coupling products were easily isomerized to themodynamically stable mono-Cr(CO)_3-complexed biaryls under the thermal conditions. The overall process can be considered to be an enantioselective preparation of both axially chiral biaryls starting from a single planar chiral (arene) chromium complex. This stereoselective formation method of axial chiral biaryls utilizing the planar chiral arene chromium complexes can be applied for the total synthesis of biologically active natural product (-) -steganone.Enantiomerically pure (o-substituted benzaldehyde) Cr(CO)_3 complexes were treated with samarium diiodide (II) to produce a single bis-tricarbonylchromium-complexed diphenyl ethane 1,2-diols with threo configuration.The two relative stereochemistries at the benzylic position were controlled by its adjacent planar chrality of arene ring. Similarly, treatment of enantiomerically pure tricarbonylchromium complexes of o-substituted phenyl aldimines with samarium diiodide gave enantiomerically 1,2-diamines after oxidative de-metalation. Less