[EN] GALACTOSE-LINKED MULTIMERIC GLYCOMIMETIC INHIBITORS OF E-SELECTINS, GALECTIN-3, AND/OR CXCR4 CHEMOKINE RECEPTORS [FR] INHIBITEURS GLYCOMIMÉTIQUES MULTIMÈRES LIÉS AU GALACTOSE DE SÉLECTINES E, DE GALECTINE-3 ET/OU DE RÉCEPTEURS DE CHIMIOKINE CXCR4
New methods for reductive free-radical cyclizations of α-bromoacetals to 2-alkoxytetrahydrofurans with activated chromium(II)-acetate
作者:Claus Hackmann、Hans J. Schäfer
DOI:10.1016/s0040-4020(01)81285-0
日期:1993.5
free-radical cyclization of α-bromoacetals 4 to 2-alkoxytetrahydrofurans 5 in 54–93% yield induced by activated chromium(II)-acetate. Four new methods have been developed in order to activate the transition metal. Two of them require only catalytic amounts of chromium(II)-acetate, because it can be regenerated in situ chemically or electrochemically. The diastereoselectivity of the cyclization depends on
Palladium-catalysed conversion of alkenols into five- and six-membered ring lactones at room temperature and atmospheric pressure
作者:Howard Alper、Danielle Leonard
DOI:10.1039/c39850000511
日期:——
Unsaturated alcohols react with carbon monoxide, oxygen, palladium chloride, copper(II) chloride, and hydrochloric acid in tetrahydrofuran to give lactones in 42–80% yield.
Highly regioselective intramolecular hydroxymethylation of α,β-unsaturated carboxylic acids
作者:Torsten Linker、Michael Maurer、Frank Rebien
DOI:10.1016/0040-4039(96)01931-4
日期:1996.11
A convenient synthesis of hydroxy esters 7 and lactones 8 by starting from easily available α,β-unsaturated carbocyclic acids 4 is described. The key step of this transformation is a hitherto unknown radical cyclization of silyl esters, which exhibits a high degree of regioselectivity through steric and orbital control.
The reductions of an α, β-unsaturated lactone (5) and lactam (7) with the Ni2+/BH-4 system resulted in the formation of cis-hydrogenated products (8a and 9a) with high stereoselectivity. The cis products (8a and 9a) were easily isomerized to the corresponding trans isomers (8b and 9b, respectively) by refluxing with sodium methoxide in anhydrous methanol. Isotope labeling studies with methyl cinnamate as the substrate indicated that the reduction with this reducing system poceeds stepwise via a carbon-nickel intermediate.
The First Stereoselective Palladium-Catalyzed Cyclocarbonylation of β,γ-Substituted Allylic Alcohols
作者:Melanie Brunner、Howard Alper
DOI:10.1021/jo9702709
日期:1997.10.1
beta,gamma-Substituted allylic alcohols react with CO in the presence of catalytic quantities of palladium acetate and 1,4-bis(diphenylphosphino)butane affording alpha,beta-substituted-gamma-butyrolactones in 42-85% isolated yields. The complete stereoselectivity observed in some cases is a significant feature of the lactonization reaction, with (E)-allylic alcohols affording trans-disubstituted lactones. Depending on the structure of the allylic alcohol used in the cyclocarbonylation reaction, the formation of the corresponding alkene or the beta,gamma-unsaturated carboxylic acid was observed as a side or the principal reaction.