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| - Stereoselective Synthesis of Both Enantiomers of Axially ChiralBiaryls Utilizing Planar Chiral Tricarbonyl(arene)chromiumComplexes
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| - Tricarbonyl(2,6-disubstituted 1-bromobenzene)chromiumcomplexes were treated with ortho-substituted arylboronic acids in the presence of Pd(0) catalyst togive mono Cr(CO)3 complexes ofbiphenyl compounds with complementary axial chirality, with extremelyhigh stereoselectivelydepending upon the steric bulkiness of the orthosubstituents. Cross-coupling of o-alkyl-orhydroxymethyl-substituted phenylboronic acids with (arene)chromiumcomplexes diastereoselectively gave Cr(CO)3-complexed biaryls in which theortho substituents are in a syn-orientationtothe tricarbonylchromium fragment. With o-formylphenylboronic acids, diastereoisomeric anti-coupling products were stereoselectively obtained. The kineticallycontrolled coupling productswere easily isomerized to thermodynamically more stablemono-Cr(CO)3-complexed biaryls bymodification of the o-substituents to less hindered ones, orthe thermal conditions assisted theaxial isomerization. The overall process can be considered to bean enantioselective preparationof both axially chiral biaryls starting from a single planar chiral(arene)chromium complex.
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