Asymmetric catalysis / Copper-Schiff base complexes, chiral Synthesis of Optically Active Siloxycyclopropanes by Asymmetric Catalysis, I. -Influence of the Catalyst on the Cyclopropanation of (3-1-Phenyl-1-(trimethylsi1oxy)prop-1-ene
The cyclopropanation of silyl enol ether l a with methyl diazo-propanations of silyl enol ethers with easily available copperacetate (2a) and diazoesters 2b-d in the presence of optically Schiff base catalysts. The ring opening of the separated diaactive copper salicylimine complexes 4-Cu was systematically stereomers of 3a employing nBu,NF provided methyl y-oxostudied. Up to 88% enantiomeric excess in products 3 were carboxylate 6a in good optical purity. This demonstrates that obtained by employing the appropriate reaction conditions this process occurs without racemization and also that 3a is and the optimal catalyst ligands. Thus, for the first time re-formed with the same absolute configuration at C-1. spectable optical yields were achieved in asymmetric cyclo-
l a 2a 3a Darstellung der chiralen Katalysatorliganden Als Katalysatoren der enantioselektiven Cyclopropanierungsreaktion wurden in dieser Arbeit Kupfer(I1)-Komplexe chiraler Salicylaldimine 4 eingesetztL5]. Katalysatoren dieses Typs waren zuerst von Aratani et al. [61 zur enantioselektiven Cyclopropanierung von Olefinen verwendet worden. Diese Kupferkomplexe wurden dabei von uns in situ aus den ent-