Search results for "diastereomer"
showing 10 items of 149 documents
1H NMR and IR spectra of methyl dichloropropanoates and butanoates
1981
Abstract Methyl dichloropropanoates and butanoates were synthesized and their 1H NMR and IR spectra were studied. Comparisons were made with the spectral characteristics of corresponding monochlorocompounds. Special attention was given to the elucidation of the characteristic spectral features associated with particular chlorine substitution patterns. The 1H NMR of erythro and threo methyl 2,3-dichlorobutanoates were analyzed using a computer program MAOCON, a modified LAOCOON 3 program. In the spectrum of the threo form the order of the chemical shifts of protons on asymmetric carbons seems to be opposite to that reported in earlier literature. Also vicinal coupling constants J23 were foun…
Kinetic control in the chiral recognition of three-bladed propellers
2010
The ion pair of the stereolabile C(3)-symmetric, i(+)o proton complex [1H](+) of diaza-macropentacycle 1 and the configurationally stable Delta-TRISPHAT ([Delta-3](-)) anion exists in the form of two diastereomers, namely, [Delta-(1.H)][Delta-3] and [Lambda-(1.H)][Delta-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D(8)]THF (28%)CD(2)Cl(2) (22%)CDCl(3) (20%)[D(8)]toluene (16%)C(6)D(6) (7%)[D(6)]acetone (0%) at thermodynamic equilibrium. Except in the case of [D(6)]acetone, the latter is reached after a period of time that increases from 1 h ([D(8)]THF) to 24 h (CDCl(3)). Moreover, the initial value of the de of [1.H][Delta-3] in CDCl(3), before the t…
ChemInform Abstract: Synthesis and X-Ray Structure of Metalated Rhodium(II) Catalysts with a Chiral Phospholane.
2001
The reaction of Rh2(O2CR)4 (R = CH3, CF3) with the chiral phosphane (2S,5S)-2,5-dimethyl-1-phenylphospholane (PC*H), results in the formation of two diastereoisomers of Rh2(O2CCR)2(PC*)2, with (P) and (M) configuration. These can easily be isolated by chromatographic methods to obtain enantiomerically pure RhII compounds. Preliminary catalytic studies have shown that they induce moderate asymmetry in the cyclization of 5-aryl-1-diazo-2-pentanones and 1-diazo-5-hexen-2-one. X-ray analysis of the (M) diastereoisomer with formula Rh2(O2CCCH3)2(PC*)2 is reported. The crystallographic parameters are as follows: space group P21212 (orthorhombic) with a = 12.1347(11) A, b = 14.5870(13) A, c = 9.81…
Highly Enantioselective Kinetic Resolution of Michael Adducts through N-Heterocyclic Carbene Catalysis: An Efficient Asymmetric Route to Cyclohexenes
2018
Ahighly efficient strategy for the kinetic resolu-tion of Michael adductswas realized using achiral N-het-erocyclic carbene catalyst.The kinetic resolution providesanew convenientroute to single diastereomers of cyclo-hexenes and Michael adducts in good yields with highenantiomeric excesses (up to 99 % ee with aselectivityfactor of up to 458). This “two flies with one swat” con-cept allows the synthesis of these two synthetically valua-ble compound classes at the same time by asingle trans-formation. peerReviewed
Thermische Diels-Alder-Reaktionen mitN-(2-Alkenoyl)-(S)-prolinestern als chiralen Dienophilen in organischen und wäßrigen Reaktionsmedien
1990
Thermal Diels-Alder Reactions with N-(2-Alkenoyl)-(S)-proline Esters as Chiral Dienophiles Cyclopentadiene reacts with N-acryloyl-(S)-proline benzyl and allyl ester in toluene at 0°C to give the bicycloheptene-carboxylic acid amides with a stereoselection of (2S):(2R) = 81:19. In the reactions with the N,N′-fumaroylbis(proline esters) the cycloadducts are formed in high yields and with isomer ratios of up to 97:3. The absolute configuration of N,N′-〈(1R,2R,3R,4S)-bicyclo[2.2.1]hept-5-ene-2,3-diyldicarbonyl〉bis-[(S)-proline benzyl ester] (6 a) has been determined by an X-ray analysis. In the reactions of the acrylamides with cyclopentadiene and of the fumaramides with cyclopentadiene, isopre…
Preparation and structure of pyrrolo[2,1-b]- and isoindolo[1,2-b][3,1]epoxyquinazolines
2007
Abstract Various γ-oxocarboxylic acids [aroylpropionic acids, cis-2-(4-methylbenzoyl)cyclohexanecarboxylic acid, diendo-3-benzoylbicyclo[2.2.1] heptane-2-carboxylic acid, formylbenzoic acid, methanobenzenecyclooctencarboxylic acid and the cyclopentadiene adduct of 3-trans-(4-methylbenzoyl)acrylic acid] were reacted with diexo-3-aminomethyl-7-oxabicyclo[2.2.1]hept-5-en-2-ylamine 2 to result in condensed pyrroloepoxyquinazolines 3–10. The starting 2 retained the diexo configuration, but cis → trans isomerization took place when cis-2-(4-methylbenzoyl)cyclohexanecarboxylic acid was applied. The structures, including the ring annelations and the position of the aryl group on the new chiral cent…
Novel σ1 antagonists designed for tumor therapy: Structure – activity relationships of aminoethyl substituted cyclohexanes
2021
Abstract Depending on the substitution pattern and stereochemistry, 1,3-dioxanes 1 with an aminoethyl moiety in 4-position represent potent σ1 receptor antagonists. In order to increase the stability, a cyclohexane ring first replaced the acetalic 1, 3-dioxane ring of 1. A large set of aminoethyl substituted cyclohexane derivatives was prepared in a six-step synthesis. All enantiomers and diastereomers were separated by chiral HPLC at the stage of the primary alcohol 7, and their absolute configuration was determined by CD spectroscopy. Neither the relative nor the absolute configuration had a large impact on the σ1 affinity. The highest σ1 affinity was found for cis-configured benzylamines…
Ligand dynamics of tert-butyl isocyanide oxido complexes of molybdenum(IV).
2014
The six-coordinate molybdenum(IV) oxido isocyanide complex 1 [Δ,Λ-OC-6-2-3-[MoO(N(p)∩N(i))2(CN(t)Bu)]; N(p)∩N(i) = 4-tert-butylphenyl(pyrrolato-2-ylmethylene)amine] is obtained in diastereomerically pure form in the solid state, as revealed by single-crystal X-ray diffraction. In solution, this stereoisomer equilibrates with the Δ,Λ-OC-6-2-4 diastereomer 2 at ambient temperature. The stereochemistry of both isomers has been elucidated by NMR, IR, and UV/vis spectroscopy in combination with density functional theory (DFT)/polarizable continuum model and time-dependent DFT calculations. The isomerization 1 → 2 is suggested to proceed via a dissociative trigonal twist with dissociation of the …
Theoretical study of isomerism in phenoxyimine-based precursors of coordinative olefin polymerization catalysts
2010
Precursors of post-metallocene olefin polymerization catalysts, unlike their predecessors, are usually octahedral transition metal complexes with multidentate ligands. Such ligands may wrap around the central atom in many ways, thus yielding several isomeric species. For a wide range of phenoxyimine (FI) ligands with different substituents, all the theoretically predicted diastereomers of group 4 and 5 complexes are available synthetically. However, only one of the isomers is usually preferred, and this is determined by the nature of the substituents in the FI ligand. The origin and mechanism of such preference has not been completely elucidated. We attempted to describe it quantitatively o…
Synthesis, Coordination to Rh(I), and Hydroformylation Catalysis of New β-Aminophosphines Bearing a Dangling Nitrogen Group: An Unusual Inversion of…
2002
Variants of the beta-aminophosphine L(1) [Ph(2)PCH(2)CH(Ph)NHPh] containing additional nitrogen donor functions have been prepared. These functions are branched off the C atom adjacent to the P atom, or the P atom itself. Ligand [Ph(2)PCH(o-C(6)H(4)NMe(2))CH(Ph)NHPh] has been obtained as a mixture of two diastereomers L(3A) and L(3B) by lithiation of L(2) [Ph(2)PCH(2)(o-C(6)H(4)NMe(2))] with n-BuLi followed by PhCH=NPh addition and hydrolysis. The diastereomers have been separated by fractional crystallization from ethanol. Ligand Et(2)NCH(2)P(Ph)CH(2)CH(Ph)NHPh has been obtained as a mixture of two diastereomers L(5A) and L(5B)(starting with P-Ph reductive cleavage of L(1) by lithium and s…