Search results for "selective synthesis"

Enzyme-mediated enantioselective acylation of secondary amines in organic solvents

1991

Abstract Porcine pancreatic lipase (PPL) and lipase Amano P catalyze the enantioselective acylation of cyclic 1,2- and 1,3-amino alcohol derivatives in organic solvents. The enatiomeric excesses (ee′s) were shown to depend on the enzyme, reaction time, temperature and type of substrate.

Modification of Chiral Properties Due to Interaction of Polymers and Small Molecules or Ions

1979

The first part of this report deals with changes in the optical rotatory dispersion and circular dichroism resulting from the chemical modification of optically active polymers. Amylose derivatives have very different chiroptical properties compared with cellulose derivatives. Variations in glucosidic bonds and differing secondary structures are described and suggested as causes for this. The N-chlorination of synthetic optically active polyamides is also described, which in all probability proceeds without changing the configuration at the asymmetric C atoms. Reactions of inactive polymers with low molecular weight chiral reagents usually give optical rotation values proportional to the de…

Enantioselective synthesis of sabina ketone

2003

Both enantiomers of sabina ketone were efficiently prepared via an easy synthesis of 1-diazo-5-methylene-6-methylheptan-2-one, starting from succinic anhydride, followed by its highly enantioselective cyclization catalyzed by chiral dirhodium(II) compounds having ortho-metalated phosphines as ligands.

Enantioselective addition of sodium bisulfite to nitroalkenes. A convenient approach to chiral sulfonic acids

2021

An enantioselective organocatalytic addition of sodium bisulfite to (E)-nitroalkenes has been developed by using a chiral bifunctional organocatalyst. The present methodology provides a variety of chiral β-nitroethanesulfonic acid compounds (17 examples) with excellent results: up to 99% yield and excellent enantioselectivity (up to 96% ee). The reaction tolerates (hetero)aryl and alkyl substituents on the β-nitroalkenes, and β,β-disubstituted nitroalkenes.

ChemInform Abstract: A Catalyst Designed for the Enantioselective Construction of Methyl- and Alkyl-Substituted Tertiary Stereocenters.

2016

Tertiary methyl-substituted stereocenters are present in numerous biologically active natural products. Reported herein is a catalytic enantioselective method for accessing these chiral building blocks using the Mukaiyama-Michael reaction between silyl ketene thioacetals and acrolein. To enable remote enantioface control on the nucleophile, a new iminium catalyst, optimized by three-parameter tuning and by identifying substituent effects on enantioselectivity, was designed. The catalytic process allows rapid access to chiral thioesters, amides, aldehydes, and ketones bearing an α-methyl stereocenter with excellent enantioselectivities, and allowed rapid access to the C4-C13 segment of (-)-b…

ChemInform Abstract: Applications and Stereoselective Syntheses of P-Chirogenic Phosphorus Compounds

2016

Phosphorus compounds bearing chirality on the P-center are usually qualified as P-chirogenic or P-stereogenic. This chemical class concerns natural products, agrochemistry, molecular materials, biology and pharmacy, although it is certainly in coordination chemistry and in asymmetric catalysis using chiral transition metal complexes that P-chirogenic phosphorus compounds are the most used. The chiral phosphine ligands and their uses in asymmetric metal-catalyzed reactions have been widely reviewed in literature. However, an overview covering the applications as well as the stereoselective syntheses of all classes of phosphorus compounds has not yet been provided. This review reports the bes…

ChemInform Abstract: Enantioselective Syntheses of 2-Alkyl-, 2,6-Dialkylpiperidines and Indolizidine Alkaloids Through Diastereoselective Mannich-Mic…

2010

Organocatalytic enantioselective synthesis of trifluoromethyl-containing tetralin derivatives by sequential (hetero)Michael reaction–intramolecular n…

2017

The enantioselective synthesis of tetralin derivatives bearing a trifluoromethylated all‐carbon quaternary stereocenter has been accomplished through a synthetic sequence comprising an organocatalytic β‐functionalization of ortho‐1‐trifluoromethylvinyl‐(hetero)aromatic conjugated aldehydes followed by the intramolecular nitrone 1,3‐cycloaddition reaction (INCR). Both nitromethane and N‐Cbz‐hydroxylamine were employed as nucleophiles in the initial organocatalytic conjugate addition step, which provided the chiral information required for the subsequent diastereoselective INCR. Although diastereoselectivity was moderate, good yields and enantioselectivities were, in general, obtained. Intere…

Base-Dependent Stereodivergent Intramolecular Aza-Michael Reaction: Asymmetric Synthesis of 1,3-Disubstituted Isoindolines

2013

The nucleophilic addition (A(N)) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2-symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may a…

ChemInform Abstract: Enantioselective LaIII-pyBOX-Catalyzed Nitro-Michael Addition to (E)-2-Azachalcones.

2013

A [La(OTf)3] complex with a new pyBOX ligand bearing a bulky 1-naphthylmethyl substituent at the 4′-position of the oxazoline ring catalyzes the conjugate addition of nitroalkanes to a broad range of (E)-2-azachalcones, providing the expected nitro-Michael products with good yields and enantiomeric excesses up to 87 %. The optical purity of the products can be increased by a single crystallization. A plausible stereochemical model to account for the observed stereochemistry has been proposed.