Synthesis of optically active boron-silicon bifunctional cyclopropane derivatives through enantioselective copper(I)-catalyzed reaction of allylic carbonates with a diboron derivative
(Chemical Equation Presented) Two for the show: A copper(I)-catalyzed reaction forms boron-silicon bifunctional cyclopropane derivatives from γ-silylated allylic carbonates and a diboron species (see scheme). The reaction is highly enantioselective when a chiral bisphosphine ligand is used. The stereoelectronic effect of the silyl group induces unusual regioselectivity of the boryl-copper(I) addition across the C-C double bond.
Kinetic Enzymatic Resolution of Cyclopropane Derivatives
The kinetic enzymatic resolution of various cyclopropane derivatives was systematically investigated. The study focused on synthetically useful cyclopropylmethanols (e.g., 18a/j or 19a/j) as well as some rarely investigated cyclopropanols (e.g., 24/25 or 27). The combination of enantioselective catalytic or diastereoselective synthesis of enantiomerically enriched compounds with enzymatic approaches ultimately led to the most convenient route to enantiomerically pure starting materials. Again, this was especially proven for the synthesis of cyclopropanols 18a/j and 19a/j. Key to the successful investigation was to rigorously establish an analytical tool for the analysis of enantiomeric composition of reaction mixtures.
Pietruszka, Joerg,Rieche, Anja C. M.,Wilhelm, Thorsten,Witt, Andreas
p. 1273 - 1286
(2007/10/03)
Chirality transfer from silicon to carbon via diastereoselective Simmons-Smith cyclopropanation of chiral alkenylsilanols
Simmons-Smith cyclopropanation of a chiral alkenylsilanol with CH2I2-Et2Zn proceeds diastereoselectively to give the corresponding cyclopropylsilanol product. Chirality transfer from silicon to the alkenyl carbons of the silicon substituent is observed. The stereochemistry of the obtained cyclopropylsilanol is confirmed by converting to cyclopropanol via Tamao oxidation.
Diastereoselective Synthesis of Cyclopropyl Boronic Esters
The conversion of simple 1-alkynes to optically active 2-alkyl-cyclopropan-1-ols is conveniently achieved by a simple protocol. The key step is the cyclopropanation of alkenyl boronic esters derived from (4-)-diisopropyl L-tartrate and alkenyl boronic acids. It has been found that best yields could be obtained using diazomethane and palladium(II) acetate as catalyst. The systematic investigation of parameters influencing this reaction led to an improvement of the diastereoselectivity of the transformation.
Pietruszka, J?rg,Widenmeyer, Markus
p. 977 - 979
(2007/10/03)
Asymmetric Cyclopropanation of 1-Alkenylboronic Esters and Its Application to the Synthesis of Optically Active Cyclopropanols
The first asymmetric cyclopropanation of 1-alkenylboronic esters was realized by diastereofacial selective Simmons-Smith reaction of the esters modified by enantiomerically pure diols such as tetramethyltartaramide.Subsequent oxidation of the resulting cyclopropylboronates gave optically active 2-substituted cyclopropanols in 73-94percent ee.These reactive compounds possess high synthetic potential.
Imai, Toshiro,Mineta, Hiroshi,Nishida, Shinya
p. 4986 - 4988
(2007/10/02)
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