ABSTRACT
An organocatalytic enantioselective reaction of 2-methylcyclopentane-1,3-dione, nitroalkene, and α,ß-unsaturated aldehyde with the diphenylprolinol catalyst was developed to give the highly functionalized Hajos-Parrish-type ketones with five to six contiguous stereocenters and two quaternary carbon stereogenic centers with high diastereoselectivity and enantioselectivity. The structures of the adducts were unambiguously confirmed by single-crystal X-ray crystallographic analyses of the appropriate products.
ABSTRACT
An expedited method was developed for the enantioselective synthesis of dodecahydrobenz[a]indolo[3,2-h]quinolizine containing five contiguous stereogenic centers with high enantioselectivities (>99% ee). The methodology comprises a domino organocatalytic double Michael reaction and Pictet-Spengler-lactamization reaction. The structures and absolute configurations of the appropriate products were confirmed by X-ray analysis.
Subject(s)
Quinolizines/chemical synthesis , Catalysis , Crystallography, X-Ray , Cyclization , Indole Alkaloids/chemical synthesis , Indole Alkaloids/chemistry , Models, Molecular , Molecular Structure , Quinolizines/chemistry , StereoisomerismABSTRACT
The title compound, (C(2)H(8)N)(4)[Cu(C(6)H(2)N(10))(2)Cl(2)], consists of an anionic complex which is composed of a Cu(II) ion surrounded by four N atoms from two pyrazine-2,3-diylbis(1H-tetra-zol-1-ide) ligands, and two Cl(-) atoms in a trans-Cl(2)N(4) coordination geometry; the Cu(II) atom lies on a site of symmetry 2/m. The Cu-Cl distance of 2.8719â (5)â Å is long due to the Jahn-Teller distortion of the d(9) electron configuration of Cu(II) ion. The tetra-zole and pyrazine rings make an N-C-C-N torsion angle of 38.25â (17)°. The charge of the anionic complex is balanced by four dimethyl-ammonium cations, which inter-act with the anionic complexes via N-Hâ¯N and N-Hâ¯Cl hydrogen bonds.
ABSTRACT
A new method has been developed for the enantioselective synthesis of highly functionalized hydropentalenes bearing up to four stereogenic centers with high stereoselectivity (up to 99% ee). This process combines an enantioselective organocatalytic anti-selective Michael addition with a highly efficient one-pot reduction/lactonization/Pauson-Khand reaction sequence. The structures and absolute configurations of the products were confirmed by X-ray analysis.
ABSTRACT
Asymmetric formal [3+2] cycloadditions of 4-hydroxybut-2-enal, a succinaldehyde surrogate, and nitroalkenes with an organocatalyst provided cyclopentanecarbaldehydes containing four consecutive stereogenic centers with excellent enantioselectivities.
ABSTRACT
Synthesis of isochromene pyrimidinedione derivatives having five stereocenters has been achieved by a one-pot Michael-Knoevenagel condensation-inverse-electron-demand hetero-Diels-Alder reaction of α, ß-unsaturated aldehydes, olefinic nitroalkanes, and 1,3-dimethylbarbituric acid via a one-pot strategy with excellent diastereo- and enantioselectivities (up to 99% ee). The structures and absolute configurations of the products were confirmed by X-ray analysis.
ABSTRACT
A six-coordinate oxovanadium(V) thiolate complex and an eight-coordinate non-oxovanadium thiolate complex, [PPh(4)][VO(PS3'')(OCH(3))] (1) and [NEt(4)][V(PS3'')(2)] (2) (PS3'' = P(C(6)H(3)-3-Me(3)Si-2-S)(3)(3-)), respectively, have been isolated and structurally characterized. The former belongs to a limited collection of oxovanadium(V) thiolate complexes. The latter has an unusual coordination number of eight. More importantly, its consensus electronic structure derived from its spectroscopic data should be considered as the resonance forms of V(V)-thiolate and V(IV)-thiyl radical species. This implies that V(IV)-thiyl radical can maintain a stable presence in biological systems.
Subject(s)
Sulfhydryl Compounds/chemistry , Vanadates/chemistry , Vanadium Compounds/chemistry , Crystallography, X-Ray , Magnetic Resonance Spectroscopy , Models, MolecularABSTRACT
Michael addition of carbethoxymethylenetriphenylphosphorane (a Wittig reagent) to nitroalkenes, followed by a reaction with ethyl formylformate and cinnamaldehydes, or formaldehyde and cinnamaldehydes, provided the respective pentasubstituted cyclopentanecarbaldehydes bearing a quaternary carbon center and pentasubstituted cyclohexanecarbaldehydes having five contiguous stereocenters with excellent enantioselectivities (up to >99% ee).
ABSTRACT
A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and α,ß-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee).
ABSTRACT
Asymmetric domino Michael-acetalization reactions of 2-hydroxynitrostyrene and aldehydes "on water" followed by oxidation providing the cis-3,4-disubstituted dihydrocoumarins with excellent enantioselectivities (up to >99% ee). The variant with glutaraldehyde underwent a highly stereoselective domino Michael-acetalization-Henry reaction to afford the tetrahydro-6H-benzo[c]chromen-6-ones after the subsequent oxidation.
ABSTRACT
A stereoselective synthesis of fully substituted cyclopentenes has been achieved by a sequential organocatalyzed Stetter and Michael-aldol condensation of aromatic aldehydes, nitroalkenes, and α,ß-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with excellent diastereoselectivities and enantioselectivities (up to >99% ee).
ABSTRACT
The first asymmetric total synthesis of (+)-conicol has been achieved via a key step reaction involving the organocatalytic domino oxa-Michael-Michael-Michael-aldol condensation of 2-((E)-2-nitrovinyl)benzene-1,4-diol and alpha,beta-unsaturated aldehydes. Structures of the three-component domino reaction adducts, 20 and 21, including their absolute configurations, were confirmed unambiguously by X-ray analysis. Through this work, the absolute configuration of (+)-conicol was thereby elucidated.
Subject(s)
Antineoplastic Agents/chemical synthesis , Terpenes/chemical synthesis , Aldehydes/chemistry , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Catalysis , Crystallography, X-Ray , Drug Screening Assays, Antitumor , Haplorhini , Humans , Marine Biology , Molecular Conformation , Molecular Structure , Stereoisomerism , Terpenes/chemistry , Terpenes/pharmacology , Urochordata/chemistryABSTRACT
A series of V(III) complexes of varying coordination number (5, 6, and 7) all containing the PS3 ligand (PS3 = trianion of tris(2-thiophenyl)phosphine and its derivatives with other phenyl substituents) has been prepared and structurally characterized. The complexes have general formula [V(PS3)L(n)](0,-), where n = 1 (from L = Cl(-), 1-Me-Im, N(3)(-)), 2 (from L = 2,2'-bpy; counting each N of the bidentate ligand), and 3 (from L = 1-Me-Im, N(2)H(4)). The complexes have also been investigated by direct current (DC) magnetic susceptibility and high-frequency and -field electron paramagnetic resonance (HFEPR). HFEPR, supported by magnetometry, has provided accurate spin Hamiltonian parameters that describe the S = 1 spin ground state of the complexes. Of particular interest are the zero-field splitting (zfs) parameters which, together with structural data, are the empirical starting point for detailed computational studies. The computational methods included density functional theory (DFT), which was only marginally successful, and more advanced ab initio methods (CASSCF and SORCI). The zfs in these complexes is relatively small in magnitude (|D| approximately 1 cm(-1)) and is the result of multiple, often counteracting, spin-orbit coupling (SOC) and spin-spin coupling (SSC) contributions. The specific origin of each of these contributions is described in detail. The results indicate the level of electronic structure calculation possible for transition metal complexes even with multiple unpaired electrons and highly covalent, heavier atom donor ligands.
Subject(s)
Computer Simulation , Models, Chemical , Nitrogenase/chemistry , Organometallic Compounds/chemistry , Organometallic Compounds/chemical synthesis , Quantum Theory , Crystallography, X-Ray , Electron Spin Resonance Spectroscopy , Electrons , Models, Molecular , Molecular Structure , Nitrogenase/metabolism , Sulfhydryl Compounds/chemistry , Vanadium/chemistryABSTRACT
The stereoselective synthesis of all-cis 5-nitro-4,6-diphenylcyclohex-1-enecarboxylic ester has been achieved by an organocatalytic asymmetric Michael-Michael-Wittig cascade reaction of phosphorus ylides, nitroolefins, and alpha,beta-unsaturated aldehydes with excellent enantioselectivities (up to >99% ee).
Subject(s)
Cyclohexenes/chemical synthesis , Nitro Compounds/chemical synthesis , Organophosphorus Compounds/chemistry , Aldehydes/chemistry , Alkenes/chemistry , Catalysis , Crystallography, X-Ray , Cyclohexenes/chemistry , Models, Molecular , Molecular Structure , Nitro Compounds/chemistry , StereoisomerismABSTRACT
Organocatalytic Michael reaction of glutaraldehyde and 3-arylpropenal followed by the subsequent intramolecular aldol condensation provided 2-arylcyclohex-3-ene-1,3-dicarbaldehydes. Reactions with the 5-oxohexanal variant afforded the highly functionalized cyclohexenedicarbaldehydes in high diastereoselectivity and high enantioselectivity (>99% ee). Structure of the adduct 3j was confirmed unambiguously by X-ray analysis.
ABSTRACT
The highly enantioselective organocatalytic Robinson annulation of alpha,beta-unsaturated aldehydes was achieved, catalyzed by l-proline and trialkylamines and providing the formal [4 + 2] cycloaddition adducts. Additionally, in some examples in the catalysis with diarylpyrrolinol silyl ethers, the reactions afforded the [4 + 2] adducts with high enantioselectivity (>99.5% ee). The structure of the adduct, obtained from the reaction of 3-methylbut-2-enal and (E)-3-(2-nitrophenyl)acrylaldehyde, was confirmed by X-ray analysis. The absolute configurations of some [4 + 2] cycloadducts were investigated, and the methodology was applied in the synthesis of (+)-palitantin.
Subject(s)
Aldehydes/chemistry , Amines/chemistry , Cyclohexanols/chemical synthesis , Cyclohexanones/chemical synthesis , Proline/chemistry , Aldehydes/chemical synthesis , Catalysis , Crystallography, X-Ray , Cyclization , Cyclohexanols/chemistry , Cyclohexanones/chemistry , Models, Molecular , Molecular Structure , StereoisomerismABSTRACT
[reaction: see text] The first highly enantioselective organocatalyzed carbo [3 + 3] cascade cycloaddition of alpha,beta-unsaturated aldehydes is reported. Using this methodology, crotonaldehyde is converted to 6-hydroxy-4-methylcyclohex-1-enecarbaldehyde, which is used in the synthesis of (-)-isopulegol hydrate, (-)-cubebaol, and p-tolualdehyde as well as (-)-6-hydroxy-4-methyl-1-cyclohexene-1-methanol acetate, an intermediate in the total synthesis of lycopodium alkaloid magellanine. Other alpha,beta-unsaturated aldehydes give rise to chiral cyclohexadienes via formal [4 + 2] reactions.
Subject(s)
Aldehydes/chemistry , Proline/chemistry , Terpenes/chemical synthesis , Alkaloids/biosynthesis , Catalysis , Cyclization , Cyclohexane Monoterpenes , Lycopodium/chemistry , Molecular Structure , Proline/analogs & derivatives , Stereoisomerism , Terpenes/chemistryABSTRACT
Both cis- and trans-2-substituted-1,2,3,6-tetrahydro-pyridin-3-ols have been prepared via an aldol condensation-ring-closing metathesis sequence. A stereodivergent synthesis of optionally functionalized deoxyimino sugars was achieved via asymmetric dihydroxylation or epoxidation/nucleophilic substitution of these tetrahydropyridines.
Subject(s)
Deoxy Sugars/chemical synthesis , Imino Sugars/chemical synthesis , Crystallography, X-Ray , Deoxy Sugars/chemistry , Imino Sugars/chemistry , Models, Molecular , Molecular Structure , StereoisomerismABSTRACT
A variety of polycyclic ring skeletons (e.g., kigelinol, neoamphilectane, and kempene systems) can be prepared rapidly via intramolecular Diels-Alder cycloadditions (IMDA) of fulvenes. The length of the tethers and the diversity of the substituents on the fulvene core dictate the nature of the IMDA pathway. [reaction: see text]
Subject(s)
Cyclopentanes/chemical synthesis , Furans/chemistry , Polycyclic Aromatic Hydrocarbons/chemical synthesis , Crystallography, X-Ray , Magnetic Resonance Spectroscopy , Models, MolecularABSTRACT
[reaction: see text] Regioselective and stereoselective inverse-electron-demand Diels-Alder reaction of N-sulfonyl-1-aza-1,3-butadiene with fulvenes are described. The methodology provides an efficient and novel route to tetrahydro-[1]pyrindine systems.