Search results for "selective synthesis"

Enantioselective addition of Et2Zn to seven‐membered cyclic imines catalyzed by a (R)-VAPOL-Zn(II) complex

2017

Various substituted dibenzo[b,f][1,4]oxazepines underwent an enantioselective alkylation with Et2Zn catalyzed by a (R)-VAPOL-Zn(II) complex. The corresponding chiral 11-ethyl-10,11-dihydrodibenzo[b,f][1,4]oxazepine derivatives were obtained with good yields and moderate enantioselectivities. This represents the first example of enantioselective addition of Et2Zn to cyclic aldimines.

ChemInform Abstract: Enantioselective Addition of Terminal Alkynes to N-(Diphenylphosphinoyl)imines Catalyzed by Zn-BINOL Complexes.

2012

Abstract Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).

Palladium-Catalyzed C—C Coupling Reactions in the Enantioselective Synthesis of 2,4-Disubstituted 4,5-Dehydropiperidines Using Galactosylamine as a S…

2005

Abstract Stereoselective synthesis of enantiomerically pure 2,4-disubstituted piperidine derivatives, which are considered interesting pharmacophoric structures, was achieved starting with a tandem Mannich–Michael reaction sequence on O -pivaloylated N -galactosyl aldimines. Subsequent conversion of the thus formed 2-substituted dehydropiperidinones into the corresponding enol triflates was carried out by conjugate hydride addition and trapping the enolate with N , N -bis(trifluoromethanesulfonyl)aniline. Their Suzuki–Miyaura coupling with aryl and heteroaryl boronic acids was performed under conditions compatible with the carbohydrate structure, in particular, with the sensitive N -glycosi…

Organocatalyticanti-Selective Mannich Reactions with Fluorinated Aldimines: Synthesis ofanti-γ-Fluoroalkyl-γ-amino Alcohols

2009

The asymmetric Mannich reaction between fluoroalkyl aldimines and aldehydes catalyzed by α,α-diphenylprolinol trimethylsilyl ether is reported. The corresponding Mannich adducts were reduced in situ to afford anti-β-alkyl-γ-fluoroalkyl-γ-amino alcohols in moderate yields and with very high diastereo- and enantioselectivities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Enantioselective Organocatalysis of Strecker and Mannich Reactions Based on Carbohydrates.

2007

Efficient organocatalysts for enantioselective Strecker and Mannich reactions were constructed from glucosamine as a readily accessible chiral scaffold. A variety of aromatic aldimines were subjected to hydrocyanation with good to excellent yield (72–98 %) and, in part, high enantioselectivity (69–95 % ee). Influence of the catalyst architecture on the enantioselectivity obviously arises from restrictions imposed on the conformational flexibility of the monosaccharidic backbone. In the asymmetric Mannich reaction moderate yields (up to 76 %) and enantioselectivities (up to 58 % ee) have been achieved with the described catalyst.

Enantioselective addition of terminal alkynes to N-(diphenylphosphinoyl)imines catalyzed by Zn–BINOL complexes

2012

Abstract Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).

Asymmetric Synthesis of Fluorinated Monoterpenic Alkaloid Derivatives from Chiral Fluoroalkyl Aldimines via the Pauson‐Khand Reaction

2020

Enantioselective Synthesis of α-Quaternary Amino Acids by Alkylation of Deprotonated α-Aminonitriles.

2015

A series of α-quaternary arylglycines were prepared in high optical purity (up to 98% ee) by α-alkylation of deprotonated α-aminonitriles derived by the Strecker reaction from (4S,5S)-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane. The procedure includes only chromatographic purification of the final products and is devoid of chromatography or crystallization operations on intermediates to raise the optical purity.

Total Synthesis of (-)-C/D-cis-De­hydro-3-O-methyl-estradiols

2015

A convergent synthesis of (–)-dehydro-3-O-methyl-C/D-cis-estradiol started from stereochemically defined substituted optically active 3-(2-arylethyl)-γ-butyrolactones. Regioselective bromination of the anisyl moiety, reductive ring opening of the iodolactone, and protecting-group changes led to a Weinreb amide. This then underwent an intramolecular Grignard reaction closing the B-ring to give a tetralone with defined configuration. Introduction of C-11 through an allyl Grignard addition and subsequent ring-closing metathesis gave a tetrahydro phenanthrene derivative. Oxidation of the side-chain alcohol resulted in the key aldehyde group, and a final samarium-diiodide-mediated reductive D-ri…

Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions

2016

A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.