نتایج جستجو برای: diastereoselectivity
تعداد نتایج: 565 فیلتر نتایج به سال:
The asymmetric anti-aldol addition of ketone-derived donors and aldehyde acceptors is described. Asymmetric induction is achieved through the use of chiral N-amino cyclic carbamate (ACC) auxiliaries. The transformation exhibits essentially perfect anti-diastereoselectivity and enantioselectivity, and has the unusual feature of proceeding via thermodynamic, rather than kinetic control.
A new class of chiral tetrahedral iron(II) cages were prepared from subcomponent self-assembly with high diastereoselectivity. The cages can be interconverted through imine exchange. The chiral cages displayed a spin transition close to room temperature, and the transition temperatures were affected by the substituent and uncoordinated solvents.
C-glucosyl, mannosyl and galactosyl 2-iodopropane, readily obtained from the corresponding C-glycosyl ketones, were coupled with (+)- or (-)-camphorsultam glyoxylic oxime ether with diastereoselectivity ranging from 70:30 to 80:20. C-glucosyl allothreonine was obtained by cleavage of the camphorsultam moiety.
Diastereoselective allylation and crotylation of N-tert-butanesulfinyl imines with allylic alcohols.
The palladium-catalyzed allylation of N-tert-butanesulfinyl imines with allylic alcohols in the presence of InI as reducing reagent takes place with high diastereoselectivity in reasonable yields. The reaction with crotyl alcohol is totally regioselective, leading to the anti-diastereomer as the main reaction product.
Addition of anions derived from dialkyl methylphosphonates to (Ss)-N-tert-butanesulfinyl (3,3,3)-trifluoroacetaldimine afforded (Ss,R) addition adducts in moderate to good yield (53-75%) with excellent diastereoselectivity (94-95% de). After selective removal of the N-sulfinyl group, dipeptides containing enantiomerically pure diethyl 2-amino-3,3,3-trifluoropropylphosphonate were synthesized to...
The asymmetric aza-Diels-Alder reaction of chiral imines with Danishefsky's diene in chiral ionic liquids provides the corresponding cycloadduct with moderate to high diastereoselectivity. The reaction has proved to perform better at room temperature in ionic liquids without either Lewis acid catalyst or organic solvent. Chiral ionic liquids are recycled while their efficiency is preserved.
Asymmetric alkylation of enantiomeric tetrahydroisoquinolyl oxazolines was achieved with 96-97% diastereoselectivity. Removal of the oxazoline chiral auxiliary and further transformations provide a straightforward synthesis of the two synthetic intermediates that were previously synthesized by resolution, and which comprise a formal synthesis of berbamunine by Ullman coupling.
An efficient one-pot synthesis of N-aryl[3,4-d]pyrazolopyrimidines in good yield and under mild reaction conditions is described. By exploiting electron-deficient hydroxylamines, the substituted oxime products were formed with very high E-diastereoselectivity. The key step utilizes a cyclization reaction upon an oxime derived from hydroxylamine-O-sulfonic acid to form the N-N bond of the product.
Chiral aryl methyl sulfoxides proved to be efficient activators in the asymmetric allylation of aldehydes with allyl trichlorosilanes. High enantioselectivity was found in the case of electron-poor aldehydes. The high levels of diastereoselectivity and the detection of nonlinear effects have allowed the elucidation of some mechanistic aspects of the reaction.
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