Acces aux [pyridyl-2′]-2 phosphorines

An optimized phosphole-phosphorin conversion procedure has been used for preparing the first known 2-(2′-pyridyl)phosphorin from 1-phenyl-3,4-dimethylphosphole and picolinic acid chloride.     

Asymmetric synthesis and the novel retro Diels–Alder reaction of a P-chiral sulfonyl-substituted phosphanorbornene

An asymmetric Diels–Alder reaction between phenylvinylsulfone and 1-phenyl-3,4-dimethylphosphole in the presence of a chiral organometallic reaction promoter generates the corresponding P-chiral sulfonyl-substituted phosphanorbornene which is found to undergo the facile cycloreversion reaction under mild conditions.     

Enantiopure 1-phosphanorbornadiene-2-carboxaldehydes

The reaction of phenylpropargyl aldehyde diethyl acetal with 1-phenyl-3,4-dimethylphosphole at 140°C or 1,2,5-triphenylphosphole at 170°C leads, after deprotection, to the corresponding 1-phosphanorbornadiene-2-carboxaldehydes 3 and 4 in 88 and 45% yields, respectively. The resolution of 3 and 4 was carried out by chromatography or fractional crystallization of the acetals derived from (S,S)-1,2-diphenylethane-1,2-diol. The absolute configurations were established by X-ray analysis of one of these acetals or of a 2-bromomethyl derivative.     

1-Methyl-2-vinylpyrrole and 1-phenyl-3,4-dimethylphosphole: their coordination chemistries and reactivities in a chiral palladium complex promoted asymmetric Diels–Alder reaction

Coordinated 1-phenyl-3,4-dimethylphosphole in the chiral complex chloro{(S)-1-[1-(dimethylamino)ethyl]naphthyl-C²,N}[1-phenyl-3,4-dimethylphosphole-P]palladium behaves as an activated cyclic diene in the inter-molecular Diels–Alder reaction with 1-methyl-2-vinylpyrrole to give a pair of diastereomeric P-chiral endo-cycloadducts. The diastereomeric palladium complexes could be separated by fractional crystallization and the enantiomerically pure phosphanorbornene ligands could be liberated individually from the complexes by treatment with potassium cyanide. In contrast, the [4+2] cycloaddition reaction did not occurred under similar conditions when the chloro ligand in the phosphole complex was replaced with a perchlorato ligand.     

Comparison of AM1 and PM3 semiempirical to ab initio methods in the study of Diels-Alder reactions of butadiene and cyclopentadiene with cyanoethylenes

Assuming a concerted synchronous mechanism with one transition state of the Diels-Alder reactions, the structures of the transition states and the activation energies for the reactions of butadiene and cyclopentadiene with cyanoethylenes were calculated by AM1 and PM3 semiempirical methods. The structural parameters were compared with those obtained by high level Gaussian calculations, whereas the activation energies were compared both with the ab initio calculations and those obtained experimentally. The structural properties calculated with PM3 methods are in general in better agreement with the ab initio calculations. The low level ab initio calculations are in many cases worse than the semiempirical methods. All predicted activation energies with both semiempirical methods are up to 300% higher than the experimental values. The predicted reactivity is also opposite to the experimental data. Only the very high level Gaussian calculations are in good correlation with experimental results. The predicted selectivity of the reaction is also opposite to the experimental facts. Two explanations are offered for this discrepancy: AM1 and PM3 methods cannot handle the calculation of the concerted Diels-Alder transition states and are not recommended to be used for that purpose, or this Diels-Alder reaction is not concerted but is stepwise.     

Reaction of 4,5-diamino-3-methyl-1-phenylpyrazole with 3-dimethylaminopropiophenones. Synthesis of new 4-aryl-6-methyl-8-phenyl-2,3-dihydropyrazolo[3,4-b]diazepines and 4-aryl-8-methyl-6-phenyl-2,3-dihydropyrazolo[4,3-b]diazepines

New 4-Aryl-6-methyl-8-phenyl-2,3-dihydropyrazolo[3,4-b]diazepines and 4-aryl-8-methyl-6-phenyl-2,3-dihydropyrazolo[4,3-b]diazepines were obtained from the reaction of 4,5-diamino-3-methyl-1-phenylpyrazole 1 with one equivalent of the 3-dimethylaminopropiophenones 2 in absolute ethanol. The structures of 4-aryl-6-methyl-8-phenyl-2,3-dihydropyrazolo[3,4-b]diazepines 3 and 4-aryl-8-methyl-6-phenyl-2,3-dihydropyrazolo[4,3-b]diazepines 4 were determined by detailed nmr measurements.     

AM1 semiempirical computational analysis of the homopolymerization of spiroorthocarbonate

Spiroorthocarbonates (SOCs) are monomers that have been shown to expand when homopolymerized. SOCs are potential monomer systems that can be combined with other monomers such as epoxy resin to produce a non-shrinking dental matrix for dental composites. The purpose of this study was to use a computer model (AM1) to study possible homopolymerization pathways for several SOC monomers. The gas phase transition states of three feasible reaction mechanisms for the homopolymerization of four spiroorthocarbonate 1,5,7,11-tetraoxaspiro[5,5]undecane (TOSU) systems have been examined using the AM1 semiempirical quantum mechanical model. In addition to the base TOSU noted above, the 2,8-dimethyl, 2,4,8,10-tetramethyl, and the 3,3,9,9-tetramethyl analogs were used in this study. The results of these calculations produced the heats of reaction, activation enthalpies and transition state structures. Our calculations indicate stabilization of the transition states by electron-donating and resonance-stabilizing substituent groups. The energies of activation of all of these systems were between 24 and 38 kcal/mol and all reactions were endothermic. Further, we found that there was a significant intermolecular attraction between TOSU monomers (≈3.5 kcal/mol). When compared with experimental studies of methylated TOSU by Sakai and co-workers, our calculations agree with the preferred site of nucleophilic attack, but not with the experimental rate results. It was concluded that the homopolymerization of the unsubstituted TOSU and its derivatives studied was endothermic and that the rate of homopolymerization of TOSU depends on an intermolecular pre-association of TOSU monomer in the condensed phase.     

SYNTHESIS AND STEREOCHEMISTRY OF PENTACARBONYL(PHOSPHOLE)METAL(0)- AND TETRACARBONYLBIS(PHOSPHOLE)METAL(0) COMPLEXES OF 6B ELEMENTS

Abstract

Pentacarbonylphospholemetal(0) and cis-tetracarbonylbis(phosphole)metal(0) complexes were synthesized from the thermal reaction of M(CO)₃(THF) and M(CO)₄(COD) (M: Cr, Mo, W) with corresponding phosphole (1-phenyl-3,4-dimethylphosphole, 1-phenyl-3-methylphosphole, and 1-phenylphosphole). These complexes were isolated as orange crystals by column chromatography on silicagel at 253 K and crystallization from n-hexane at 223 K and characterized by means of IR and NMR (¹H, ¹³C, and ³¹P). Spectroscopic data shows that the phosphole is coordinated to the transition metal through its phosphorus atom rather than through the conjugated diene unit in the both types of complexes. The tetracarbonylbis(phosphole)metal(0) complexes were found to have cis-arrangement of two phosphole ligands. Comparing ¹³C-NMR chemical shifts of the complexes with the free ligands, one can deduce that the involvement of the phosphorus atom in the ring π-electron delocalization is drastically reduced upon coordination. This is attributed to the stronger [sgrave]-donation but weaker π-accepting ability of the phosphorus atom in the phosphole ligands compared to the carbonyl groups.     

Copolymers of carbon dioxide and nitrogen: an AM1 and ab initio computational study

Extending work by various groups on possible dimers, trimers, etc. of dinitrogen and of carbon dioxide, the authors have studied analogous copolymers of N₂ and CO₂ computationally. Twelve cyclic structures were examined with the AM1, HF/3-21G, HF/6-31G* and MP2(FC)/6-31G* methods, and the acyclic “monomer” to “tetramer” HO(C(O)O–N= N–)_nH, n=1–4, were studied at the AM1 and HF/3-21G levels; the cyclic species included 2-oxa-3,4-diazacyclobut-3-ene-1-one, 2-oxa-3,4,5,6-tetraazacyclohexa-3,5-diene-1-one, and various aza/oxa bicyclo[2.2.0] and bicyclo[2.2.2] systems. For the cyclic species, it was concluded that only the MP2(FC)/6-31G* results, which differ considerably from those at the other three levels, are likely to be reliable. These MP2 calculations indicate that only seven of the 12 cyclic structures studied are stationary points (one is a transition structure), and none of them is kinetically stable at room temperature. Although some have high energy densities (ca. 7–10 kJ g⁻¹), their expected low kinetic stabilities seems to make this of little practical value. The acyclic “copolymers” were all relative minima at the AM1 and HF/3-21G levels; unlike the cyclic species, their kinetic stabilities were not investigated directly by comparing the energies of reactants and decomposition transition states. The energy density of the infinite acyclic polymer was found by extrapolation to be 5.1 (AM1) or 5.6 (3-21G) kJ g⁻¹. The calculated vibrational spectra of the MP2 stationary points and of the acyclic molecules gave some indication of instability by the presence of low-frequency modes leading in the limit to decomposition.     

3-苯基-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑的电子结构和光谱性质的含时密度泛函理论研究

对3-苯基-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑(PATT)用量子化学密度泛函方法(DFT)在B3LYP/6-31G(d)水平上进行了几何构型的全优化, 探讨了分子电荷转移、前线轨道能量和电子光谱等性质的变化规律, 在此基础上采用含时密度泛函方法(TDDFT)计算了分子激发态的电子跃迁能. 将其与实验所得激发态的电子跃迁能结果相比, 理论计算最大相对偏差为0.071, 最小相对偏差为0.041.     

Reduction—complexation des sulfures de phosphines par les fer-carbonyles

1-Phenyl-3,4-dimethylphosphole (L) yields the classic σ complex LFe(CO)₄ with Fe₂(CO)₉ and the unsual σ,π complex LFe₂(CO)₇ with Fe₃(CO)₁₂, whereas 1-t-butyl-3,4-dimethylphosphole (L′) with Fe₃(CO)₁₂ yields L′Fe₂(CO)₆ which belongs to a type already described in the literature. With Fe₂(CO)₉ at 85°C, the phosphole sulfide LS yields the two σ and σ,π complexes directly by reduction—complexation. This Fe₂(CO)₉ reduction—complexation process works only with phosphole and phospholene sulfides. However, with Fe(CO)₅ in great excess at 150°C, a general phosphine sulfide reduction—complexation procedure takes place. A study of the displacement of 1-phenyl-3,4-dimethyl-3-phospholene (L″) from its σ complex L″Fe(CO)₄ by trimethylphosphite has shown that L″ has a greater complexing ability toward iron than the phosphite, contrary to what could be expected from the work of Tolman on nickel complexes.     

Theoretical determination of molecular structure. Conformation of some benzo[10]-annulenes and [10]-annulene

Summary The AM1 method was used to carry out a theoretical study of optimized geometries and energies of some benzoannulenes. The transition state of the transformation of the benzo[10]annulene was also determined. The transition state has been located.     

Reactions of α,β-unsaturated ketones with cyanoacetamide

3-Aryl-1-phenyl-2-propen-1-ones Ia-f and aroylphenylacetylenes Va-d reacted under reflux for 3 hours with cyanoacetamide in the presence of sodium ethoxide to give the corresponding 4-aryl-3-cyano-6-phenyl-2-(1H)pyridones VI. However, when ketones Ia-e were refluxed with cyanoacetamide for one hour in the presence of sodium ethoxide or piperidine, they gave the corresponding 4-aryl-3-cyano-3,4-dihydro-6-phenyl-2-(1H)pyridones IIIa-e, which upon heating with selenium gave the corresponding 2-pyridones VI. The structures of the products are based on chemical and spectroscopic evidence.     

Crystal Structures of 5-Nitro- and 5-Ethoxycarbonyl-Substituted 6-Phenyl-4-(3-fluorophenyl)-3,4-dihydro-(1H)-pyrimidin-2-ones

The crystal structures of 5-nitro- and 5-ethoxycarbonyl-substituted 6-phenyl-4-(3-fluorophenyl)-3,4-dihydro-(1H)-pyrimidin-2-ones were determined by X-ray diffraction analysis. Conformational peculiarities of the structures have been revealed and compared with data for other biologically active dihydropyrimidinones.     

Am1 and pm3 transition structure for the hydride transfer. A model of reaction catalyzed by dihydrofolate reductase

The transition state structure for the hydride transfer in dihydrofolate reductase, DHFR, enzyme has been calculated with analytical gradients at semiempirical levels: AM1 and PM3. The geometry, electronic structure and transition vector components are qualitatively semiempirical level independent. Comparing the transition structures for the hydride transfer step in models of liver alcohol dehydrogenase, formate dehydrogenase, lactate dehydrogenase, and glutathione reductase, the geometries of these stationary points are transferable and invariant. The topology of the transition structures in these enzymes resembles the one calculated in this paper.     

Semiempirical and ab initio transition state calculations for the transformation of N-acetyltetrazoles into corresponding 1,3,4-oxadiazoles

The transformation of 2-acetyl-5-substituted-tetrazoles into the corresponding 1,3,4-oxadiazoles was studied with the semiempirical and ab initio methods. Two mechanisms, one with two transition states and the other with three, were elucidated by . The first mechanism supported by PM3 and MNDO has a two-step, almost concerted, mechanism for the elimination of a nitrogen molecule from the tetrazole ring and formation of the oxadiazole product from an open-chain intermediate through carbon C₅ and acetyl oxygen bond formation. The second mechanism supported by AM1 and MINDO/3 breaks the elimination of the nitrogen molecule into two steps: first breaking the N₄-C₅ and then the N₂-N₃ bonds. Even when the AM1 and MINDO/3 transition state structures were optimized by PM3 and MNDO, the obtained transition states present only one bond breaking. The HF/STO-3G and HF/3-21G ab initio methods agree with the first mechanism where two bonds are breaking almost simultaneously. Despite the disagreement in the mechanism of the nitrogen elimination, the transition state that presents the product formation from open-chain intermediates is quite similar for all methods studied. The semiempirical calculation of this transition state is possible only if it is assumed that it has biradical character. The activation energies calculated by PM3 seem to be insensitive to the nature of the substituents.     

Chemistry of the pyrazolidines. 26. Alkylation of 4-benzyliden-1-phenyl-3.5-dioxopyrazolidines

The reaction of 4-benzyliden-1-phenyl-3,5-dioxopyrazolidines with alkyl halides in the presence of sodium alkoxide gave 1-phenyl-2-alkyl-4-benzyliden- and 1-phenyl-2,4-dialkyl-4-(-alkoxybenzyl)-3,4-dioxopyrazolines. The structures of these compounds were confirmed by UV, IR, and PMR spectroscopy, and by mass-spectrometry.For communication 25 see [1].Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 2, pp. 222–226, February, 1986.     

Computational and experimental studies of the conformational reactions of 1,3,5-tris(pentaphenylphenyl)benzene

Computational analyses of the five possible functional group rotations in 1,3,5-tris(pentaphenylphenyl)benzene (1) were conducted at three disparate levels of theory: AM1, HF/STO-3G, and B3LYP/6-31G(d). The ground state and transition state structures were located for all of the conformational reactions, and the free energies of activation for these processes were calculated. In addition, compound 1 was resolved by low-temperature chromatography on a chiral support, and its barrier to racemization was determined by dynamic chromatography. These computational and experimental results are compared with data from dynamic NMR studies of 1 in the literature.     

C–N rotational barriers in aromatically substituted styrylformamides: an AM1 study utilizing the conductor like screening model for real solvents

Semi-empirical calculations at the AM1 level utilizing the Conductor Like Screening Model for Real Solvents (COSMO-RS) are performed on a series of styrylformamides in their E, Z and transition state conformations to determine barriers to rotation (BIR) about the amide bond. Comparison is made with experimental data from two-dimensional exchange correlation spectroscopy NMR experiments (2D EXSY). Equilibrium and transition state structures are analyzed to explain the observed decrease in rotational barriers with electron withdrawing substituents. Calculations of nonexperimentally determined structures are performed to predict rotational barriers. The theoretically observed trends correspond well with chemical intuition.     

Selenium heterocycles. XXXII . Synthesis of [1]benzoxepino[3,4-d]-thiazole, [1]benzothiepino[3,4-d]thiazole, [1]benzoxepino[3,4-d]selenazole,and [1]benzothiepino[3,4-d]selenazole. four novel heterocycles

Starting from the readily available ethyl 2-phenyl-4-methyl-thiazole-5-carboxylate (III), 2-phenyl-4-chloromethyl-thiazole (VIII) and 2-aryl-4-chloromethylselenazole (XIV), 2-phenyl-4,10-dihydro-10-oxo-[1]benzoxepino[3,4-d]thiazole (Ia), 2-phenyl-4,10-dihydro-10-oxo[1]benzothiepino[3,4-d]thiazole (Ib), 2-aryl-4,10-dihydro-10-oxo[1]benzoxepino[3,4-d]selenazoles (IIa-IIe) and 2-aryl-4,10-dihydro-10-oxo[1]benzothiepino[3,4-d]selenazoles (IIf-IIj) were prepared.