Preparation of Aliphatic Ketones through a Ruthenium-Catalyzed Tandem Cross-Metathesis/Allylic Alcohol Isomerization
作者:David Finnegan、Benjamin A. Seigal、Marc L. Snapper
DOI:10.1021/ol060918g
日期:2006.6.1
shown to be effective catalysts for cross-metatheses of allylic alcohols with cyclic and acyclic olefins, as well as isomerization of the resulting allylic alcohols to alkyl ketones. The net result of this new tandem methodology is a single-flask process that provides highly functionalized, ketone-containing products from simple allylic alcohol precursors. [reaction: see text]
The elimination of thiocyanic acid from the stereoisomers of the hex-3-ene-2,5-diyl dithiocyanates, 4a, 4b, 6a and 6b, in the presence of a strong neutral base in an organic solvent, yields mixtures of the hex-2,4-dien-2-yl thiocyanates 9, 10 and 11via a preferentially syn process.
The catalytic asymmetric hydrogenation of prochiral ketones was carried out with Ru(II) complexes prepared from new chiral diphosphine ligands, cis-(R,R)-2,5-bis[(diarylphosphino)]-3-hexenes. These new ligands were prepared from enantiornerically pure (R,R) or (S,S)-(Z)-3-hexene-2,5 diol and enantionteric excesses up to 85% were obtained in the reduction of 2-benzamidomethyl-3-oxobutanoate, starting material for the synthesis of 4-acetoxy-2-azetidinone. (c) 2007 Elsevier Ltd. All rights reserved.
Stereodivergent Approach to β-Hydroxy α-Amino Acids from <i>C</i><sub>2</sub>-Symmetrical Alk-2-yne-1,4-diols
[GRAPHICS]A new stereodivergent route to erythro- and threo-beta-substituted serines from a common G-symmetrical alk-2-yne-1,4-diol is described. Stereocontrol in such an acyclic system is achieved by taking advantage of symmetry. Stereoselective alkyne reduction to either (Z)- or (E)-olefin allows selection of the stereochemistry of cc-carbon in the final amino acid by using a Pd(0)-catalyzed process. This strategy has been applied to the synthesis of (2S,3S)-3-hydroxyleucine.