90288-85-0Relevant academic research and scientific papers
Synthesis of Optically Active Siloxycyclopropanes by Asymmetric Catalysis, I. - Influence of the Catalyst on the Cyclopropanation of (Z)-1-Phenyl-1-(trimethylsiloxy)prop-1-ene
Dammast, Franziska,Reissig, Hans-Ulrich
, p. 2449 - 2456 (2007/10/02)
The cyclopropanation of silyl enol ether 1a with methyl diazoacetate (2a) and diazoesters 2b-d in the presence of optically active copper salicylimine complexes 4-Cu was systematically studied.Up to 88percent enantiomeric excess in products 3 were obtained by employing the appropriate reaction conditions and the optimal catalyst ligands.Thus, for the first time respectable optical yields were achieved in asymmetric cyclopropanations of silyl enol ethers with easily available copper-Schiff base catalysts.The ring opening of the separated diastereomers of 3a employing nBu4NF provided methyl γ-oxocarboxylate 6a in good optical purity.This demonstrates that this process occurs without racemization and also that 3a is formed with the same absolute configuration at C-1. - Key Words: Cyclopropanecarboxylates, 2-silyloxy, methyl / Cycloaddition / Enantioselectivity / Asymmetric catalysis / Copper-Schiff base complexes, chiral
Synthesis of Optically Active Siloxycyclopropanes by Asymmetric Catalysis, II. - Influence of the Silyl Enol Ether Structure on the Enantioselective Cyclopropanation with Methyl Diazoacetate
Dammast, Franziska,Reissig, Hans-Ulrich
, p. 2727 - 2732 (2007/10/02)
On the basis of reactions of (Z)-1-phenyl-1-(trimethylsiloxy)-1-propene (1a) with methyl diazoacetate (2) in the presence of different chiral (Schiff base) copper catalysts 4-Cu we extended our study of the silyl enol ethers 1b-1j.The highest enantiomeric excesses were obtained in most cases with catalyst 4b-Cu.Whereas cyclopropanations of 1-aryl- and 1-alkenyl-substituted silyl enol ethers 1b-1h gave moderate to good enantioselectivities (up to 80percent ee), alkyl-substituted olefins 1i and 1j provided less satisfactory results.By deprotonation and alkylation of 3c, 3h, and 3i it could be established that for these cyclopropanes the predominating absolute configuration of cis- and trans-cyclopropanes is equal at C-1, but consequently opposite at C-2.The influence of the silyl enol ether structure on the enantioselectivities achieved is briefly discussed. - Key Words: 2-Siloxycyclopropanecarboxylates / Silyl enol ethers / Cycloaddition / Asymmetric catalysis / (Schiff base)copper complexes, chiral
Synthesis of 2-Siloxy-substituted Methyl Cyclopropanecarboxylates
Kunkel, Elisabeth,Reichelt, Ingrid,Reissig, Hans-Ulrich
, p. 512 - 530 (2007/10/02)
2-Siloxy-substituted methyl cyclopropanecarboxylates C - useful building blocks in synthesis - are obtained in great variety and with good yields from the silyl enol ethers E and methyl diazoacetate (D) under copper salt catalysis.Whereas the regiochemical and stereochemical properties of E are completely transferred to the cyclopropanes C, the stereoselectivity concerning the position of the methoxycarbonyl group is low.The 1H and 13C data used to determine the configurations of compounds C are discussed.
