S1←S0 vibronic spectra and the vapor-state molecular structure of propanal and 2-methylpropanal

The vapor-state absorption spectra have been recorded for propanal PA and 2-methylpropanal MP with path lengths up to 120 m. The initial points in the S₁S₀ electronic transitions have been identified together with various fundamental vibrational frequencies of the PA and MP conformers. They contain nonplanar aldehyde groups in the S₁ states with inversion potential barriers of about 600 cm^–1. The parameters of the internal-rotation potential functions in the S₁ states have been determined, and the corresponding potential functions in the S₀ states have been refined.Chemical Faculty, Lomonosov Moscow University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 20–25, January–February, 1993.     

DiastereoselectiveandEnantioselectiveSynthesisof(1S,2S)-2-Ethyl-1-aminocyclopropaneCarboxylicAcid

During the last decade, 1-aminocyclopropanecarboxylic acid and its derivatives (ACCS) have attracted increasing attention of organic and bioorganic chemists due to their outstanding biological properties, ranging from antimicrobial, insecticidal, plant growth and fruit ripening controls, etc.1. Moreover, the three-membered carbocycle provides building blocks of unprecedented synthetic potential because it undergoes selective ring opening, ring enlargement or cycloaddition reactions2. The mo…     

What is the best DFT functional for vibronic calculations? A comparison of the calculated vibronic structure of the S1-S0 transition of phenylacetylene with cavity ringdown band intensities

The sensitivity of vibronic calculations to electronic structure methods and basis sets is explored and compared to accurate relative intensities of the vibrational bands of phenylacetylene in the S(1)(A(1)B(2)) ← S(0)(X(1)A(1)) transition. To provide a better measure of vibrational band intensities, the spectrum was recorded by cavity ringdown absorption spectroscopy up to energies of 2000 cm(-1) above the band origin in a slit jet sample. The sample rotational temperature was estimated to be about 30 K, but the vibrational temperature was higher, permitting the assignment of many vibrational hot bands. The vibronic structure of the electronic transition was simulated using a combination of time-dependent density functional theory (TD-DFT) electronic structure codes, Franck-Condon integral calculations, and a second-order vibronic model developed previously [Johnson, P. M.; Xu, H. F.; Sears, T. J. J. Chem. Phys. 2006, 125, 164331]. The density functional theory (DFT) functionals B3LYP, CAM-B3LYP, and LC-BLYP were explored. The long-range-corrected functionals, CAM-B3LYP and LC-BLYP, produced better values for the equilibrium geometry transition moment, but overemphasized the vibronic coupling for some normal modes, while B3LYP provided better-balanced vibronic coupling but a poor equilibrium transition moment. Enlarging the basis set made very little difference. The cavity ringdown measurements show that earlier intensities derived from resonance-enhanced multiphoton ionization (REMPI) spectra have relative intensity errors.     

A Convenient Approach to the Enantiopure （1S, 2S, 4S, 5S ）- and（ 1R, 2S, 4R, 5 S ）-2,5-Bis （ phenylmethyl）-l, 4-diazabicyclo[ 2.2.2 ] -octane

Cyclodipepflde (3S, 6S )-bis (phenylmethyl) piperazlne-2,5-dione was prelmred in high yield by heating phenylalanine methyl ester in toluene under reflux. The reduction of this cydodipeptide with sodium NaBH4-BF3 in DIME gave the (2S ,SS)-bis(phenyl-methyl)plperazine, which, on heating with ethylene bromide and triethyiamine, afforded the title compounds. This methodwas proved to be generally applicable to the synthesis of C2-symmetric 2, 5-disubsiituted=l, 4-diazabicyclo [ 2.2.2 ] octanefrom the corresponding natural or unnatural amino acid esters.     

A Convenient Approach to the Enantiopure (1S,2S,4S,5S)-and (1R,2S,4R,5S)-2,5-Bis(phenylmethyl)-1,4-diazabicyclo[2.2.2]-octane

Introduction1,4 Diazabicyclo[2 .2 .2 ]octane (DABCO)wasre portedtocatalyzeorganicreactionsduetoitsstrongbasici ty .1,2 Severalchiraltrans 2 ,3 disubstitutedDABCOshavebeensynthesizedandappliedtotheasymmetricBaylis Hillmanreaction3andvicinalhydroxylation .4ThefirstsynthesisofthetitlecompoundwasreportedbySoai5from (2S ,5S) bis(phenylmethyl)piperazine (1) ,asshowninScheme 1.Butthisprocedureislengthy ,andtheoverallyieldisnotsosatisfactory .Besides ,thereport edmethodforthepreparationof 1is…     

FeCl3⋅6H2O-catalyzed intermolecular-cascade cyclization of acetoacetanilide: aldehyde-tuned synthesis to valuable 2-pyridone analogues

The first ever breakthrough toward activation of β-ketoacetanilide and subsequent C-C and C-N bond-forming intermolecular-cascade cyclization processes is demonstrated by development of the unprecedented Lewis acid property of non-toxic FeCl(3)?6H(2)O. Aromatic, aliphatic, α,β-unsaturated, chiral sugar-based and chromone aldehydes were regio- and stereoselectively cyclized with acetoacetanilides toward construction of valuable N-containing highly functionalized 2-pyridones (see scheme for an example).     

Dicyano and pyridine derivatives of β-carotene: synthesis and vibronic, electronic, and photophysical properties

Density functional theory and time-dependent density functional theory calculations provide pictures of the molecular orbitals involved in the ground and excited states of two cyano derivatives of 8'-apo-β-caroten-8'-al synthesized via an acid-base-catalyzed Knoevenagel condensation reaction. Population analysis shows that the symmetry-allowed transition, S(0) ((1)A(g)) → S(2) ((1)B(u)) based on the C(2h) symmetry is a HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) π → π* transition with electron densities located mostly on the polyene chain. Calculated and actual steady-state absorption spectra show similar features with low-energy peak maxima between 550 and 600 nm.     

Enantioselective synthesis of (2S,2′R)-erythro-methylphenidate

A new approach towards the enantioselective synthesis of (2S,2′R)-erythro-methylphenidate (1) is described. The key step in the synthesis utilizes Evans' 4-substituted-2-oxazolidinone chiral auxiliary to control the diastereofacial selectivity in the hydrogenation of enamine intermediate 6, yielding the hydrogenated product 7 with excellent diastereoselectivity. Methanolysis of 7 afforded 1 with excellent enantiopurity.     

Synthesis of α-Oxoketene CyclicO,S and S,S Acetals

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Ab initio study of Eu3+–L (L=H2O,H2S,NH2CH3, S(CH3)2, imidazole) complexes

The ground states and binding energies of Eu³⁺–L (L=H₂O,H₂S,NH₂CH₃,S(CH₃)₂, imidazole) complexes has been determined using ab initio techniques. The binding is mostly electrostatic as expected. The empty f orbital is different for the S compounds, being a π-like orbital, while for the O and N containing ligands it is a σ-like orbital. However, the range in the binding energies for the different f holes is small.     

Synthesis and structural characterization of camphanates of (−)-(2S3S,3S) and (+)-(2S,3R)-4-Phenyl-3-bromo-2-butanol diastereoisomers

The X-ray crystal structures of (–)-syn-4-phenyl-3-bromo-2-butyl camphanate (I) and (+-anti-4-phenyl-3-bromo-2-butyl camphanate (II) have been determined. Thesyn diastereoisomer of bromohydrin has the (2S,3S) absolute configuration whereas theanti diastereoisomer has the (2S,3R) absolute configuration. The crystallized derivatives I and II have been obtained by the reaction of each stereoisomer of bromohydrin, synthesized by reduction with baker's yeast, with (1S)-camphanic chloride. Crystal data: (I) C₂₀H₂₅BrO₄:M _w: 409.32; orthorhombic,P2₁2₁2₁;a=11.245(3),b=12.086(1),c=14.512(4) å; Z=4; finalR=0.053 for 1819 observed reflections. (II) C₂₀H₂₅BrO₄;M _w=409.32; monoclinic, P2₁;a=11.352(1),b=6.378(1),c=14.255(2) å,=110.38(1);Z=2; finalR=0.045 for 1672 observed reflections.     

(15S,16S,19S,20R,34S)和(15R,16R,19R,20S,34S)氮杂Solamin类似物的合成

以手性四氢吡咯片段3a和3b为起始原料, 采用汇聚式合成策略, 完成氮杂Solamin类似物(threo-trans-erythro)的两个对应的光学异构体2a(15S,16S, 19S,20R, 34S)和2b(15R,16R,19R,20S, 34S)的不对称合成. 化合物的结构以及四氢吡咯片段的立体构型均通过NMR波谱解析的方法得到确证. 这两个非对映异构体具有相近的体外抗肿瘤活性.     

One-pot Synthesis and Crystal Structure of （1S,2R,3S,4R,5S）-1-Phenyl-2,4-dibenzoyl-3,5-difurylhexanol

(1S,2R,3S,4R,5S)-1-Phenyl-2,4-dibenzoyl-3,5-difurylhexanol 1 was synthesized by one-pot reaction of hypnone and furfurol in alkali H2O/EtOH solution and structurally defined to contain a chair-formed aliphatic carbocycle, on which the bulky substituents occupy the equatorial positions.     

N,S-, S-, S,S-, <S═O-, and < SO2-Substituted Dienes from Halo-1,3-Butadienes

Mono(thio)substituted dienes 1 gave 3a–g , 5 , and 7 with piperazine derivatives in dichloromethane. Hexachlorobutadiene 14 in a water-ethanol mixture in the presence of sodium hydroxide reacted with thiol 15 to give the mono(thio)substituted thioether 16 and di(thio)substituted thioether 17 . 18 was obtained from the reaction of 16 with m-CPBA in chloroform. 9 was obtained from the reaction of l,2,3,4,4-pentachloro-(1-2-hydroxyethylthio)-1,3- butadiene 8 with 47% HI, and 11 was synthesized from the reaction of 8 with concentrated H₂SO₄ and KBr. Compounds 9 and 11 gave in the reaction with m-CPBA in chloroform 10 , 12 , and 13 , respectively.     

Photochemical reactions of [(η 5-C5H5)Mn(CO)3] with Ph2P(S)(CH2) n P(S)Ph2 [n=1, dppm(S)2; 2, dppe(S)2; 3, dppp(S)2]

Six new complexes, Mn(CO)( ⁵-C₅H₅){Ph₂P(S)(CH₂) _n P(S)Ph₂}] (1a–3a) [(1a), n=1; (2a), n=2; (3a), n=3] and [Mn₂(CO)₄( ⁵-C₅H₅)₂(cis--Ph₂P(S)(CH₂) _n P(S)Ph₂)] (1b–3b) [(1b), n=1; (2b), n=2; (3b), n=3] have been synthesized by the photochemical reaction of [( ⁵-C₅H₅)Mn(CO)₃] with Ph₂P(S)(CH₂) _n P(S)Ph₂ [n=1, dppm(S)₂; 2, dppe(S)₂; 3, dppp(S)₂]. The complexes have been characterized by elemental analysis, mass spectroscopy, f.t.-i.r. and ³¹P–[¹H]-n.m.r. spectroscopy. The spectroscopic studies reveal that coordination of the ligand iscis-chelate bidentate in [Mn(CO)( ⁵-C₅H₅){Ph₂P(S)(CH₂) _n P(S)Ph₂}] (1a–3a) and cis-bridging bidentate between two metals in [Mn₂(CO)₄( ⁵-C₅H₅)₂(cis--Ph₂P(S)(CH₂) _n P(S)Ph₂)] (1b–3b).     

Facile Synthesis of (S,S)‐1,2‐Diacylamides and (S,S)‐1,2‐Diamines with C 2‐Symmetry

A series of chiral vicinal tertiary diacylamides with C ₂‐symmetry was synthesized from (S)‐α‐phenylethylamine, different aromatic aldehydes, and oxalyl chloride. The diacylamides obtained were then reduced to afford chiral vicinal diamines with C ₂‐symmetry. We propose that the diacylamides existed in four stable conformational isomers in solution because of the dihedral angle between acylamide bonds.