نتایج جستجو برای: enantiomeric excess
تعداد نتایج: 75059 فیلتر نتایج به سال:
A removable protecting group has been identified that allows the products of widely-used cross dehydrogenative couplings to be synthetically elaborated. The method can be used with enantiopure amines with no loss of enantiomeric excess. The methodology is exemplified by a new synthesis of enantiopure praziquantel, the drug used in the treatment of millions of people suffering from the neglected...
A chiral template was constructed from 7-ethynyl-1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-one by Sonogashira cross-coupling with 4,4''-diiodoterphenyl and was shown to bind the title compound strongly by hydrogen bonding resulting in enantioselectivities of up to 55% enantiomeric excess (ee) in the [4+4] anthracene photodimerization.
An enantioselective oxidative carbocyclization-borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol-type chiral phosphoric acids were superior co-catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess.
A chiral cobalt-catalyzed enantioselective aerobic oxidative kinetic resolution of (±)-α-hydroxy esters, using molecular oxygen as a sole oxidant, is reported and a maximum of selectivity factor (s) 31.9 was achieved with >99% enantiomeric excess for unreacted α-hydroxy esters.
A Cu(I)-catalyzed direct addition of alkynes to imines was developed. The process is simple and provides a diverse range of propargylamines in high enantiomeric excess and good yield both in water and in toluene. The absolute configuration of such addition products has been determined by x-ray crystallography.
Scalemic bromonium ions generated enantiospecifically by the action of catalytic triflic acid on scalemic regioisomeric bromohydrin derivatives are trapped intramolecularly, enantiospecifically and regioselectively to give bicyclic brominated carbocycles in excellent yield and high enantiomeric excess. This enantiospecific pathway is not significantly perturbed by the addition of a trisubstitut...
3-Alkenyl and heteroaryl chloroalcohols have been obtained in excellent enantiomeric excess (>99%) by enzymatic kinetic resolution using the haloalcohol dehalogenase HheC. Yields were close to the theoretical maximum for all substrates employed. Furthermore, the applicability of this methodology on multigram scale has been established.
In this communication, we document a facile kinetic glycosylation resolution of racemic tetrahydroberberrubine. We also demonstrate that the enantiomeric excess of the resolved products is increased via a second resolution of the minor product of the first glycosylation resolution. This provides a rare example of tandem kinetic resolution of racemates.
Asymmetric addition under mild conditions of dialkyl phosphites on aldimines derived from cinnamaldehyde catalyzed by the inexpensive chiral organocatalyst (R)-3,3'-[4-fluorophenyl](2)-1,1'-binaphthol phosphate has been found effective to give new alpha-amino-phosphonates 9 in moderate yields (30-65%) and enantiomeric excess (8.4%-61.9%).
Access to P-chiral H-phosphinates via desymmetrization of hypophosphite esters was investigated. The use of chiral auxiliaries, chiral catalysts, and of a bulky prochiral group that could lead to kinetic resolution was explored. A chiral NMR assay for enantiomeric excess determination of H-phosphinates was developed. An asymmetric route to C-chiral H-phosphinates is also examined and an assay w...
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