虾青素的合成

以α-紫罗兰酮为起始原料, 采用2C₁₅＋C₁₀→C₄₀路线合成了虾青素. 并经过选择性环氧化三甲基硅基烯醇醚双键的关键步骤, 设计并完成了关键中间体C₁₅部分——6-羟基-3-(3-羟基-3-甲基-1,4-戊二烯)-2,4,4-三甲基-2-环己烯-1-酮的合成.     

Direct determination of the equilibrium constant and thermodynamic parameters in the reaction of pentadienyl radicals with O2

Reaction of pentadienyl radicals (C₅H₇) with O₂ has been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. These radicals could be generated either by the photolysis of 1,3-pentadiene or by the two-step reaction of carbon tetrachloride photolysis followed by the H-atom abstraction reaction of Cl atom with 1,4-pentadiene. The equilibrium between pentadienyl radicals, O₂ and pentadienylperoxy radicals could be observed over the range 268–308 K. An analysis of the temporal signal of pentadienyl radicals was used to evaluate the equilibrium constant. Third-law analysis was used to evaluate the enthalpy change for the reaction C₅H₇ + O₂ ⇌ C₅H₇O₂. The observed CO bond energy in the C₅H₇O₂ adduct was found to be 56.0 ± 2.2 kJ·mol^–1, which is lower than the values of peroxy radicals formed with allyl and cyclohexenyl radicals which have an allylic resonance structure.     

Influence of monomer structure on chemo- and stereoselectivity of 1,3-diene polymerization

MAO/CpTiCl₃ is an active catalyst for the polymerization of various types of 1,3-dienes. Butadiene, (E) - and (Z) −1,3-pentadiene, (E) −2-methyl-1,3-pentadiene and 2,3-dimethylbutadiene yield, at room temperature, polymers with a cis-1,4 or a mixed cis/1,2 structure. 4-Methyl-1,3-pentadiene and (E,E) −2,4-hexadiene give, respectively, a 1,2 syndiotactic and a trans-1,4/1,2 polymer. MAO/CpTiCl₂·2THF and MAO/(CpTiCl₂)_n are less active than the CpTiCl₃ catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)-1,3-pentadiene: a cis-1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis-η⁴ at +20°C and may be trans-η² at −20°C. Results obtained with catalysts from CpTi(OBu)₃ and Ti(OBu)₄ are reported for comparison. An interpretation is given of the formation of cis-1,4 isotactic poly(2-methylpentadiene) and of 1,2 syndiotactic poly(4-methylpentadiene), as well as of syndiotactic polystyrene.     

Isomer distinction by ion/molecule reactions in an ion trap: The case of C5H8

Isomeric C₅H₈ compounds are distinguished by monitoring the products of their reactions with mass-selected ions generated from the individual isomers. This procedure, done by selecting appropriate reaction times in a quadrupole ion trap, yields data for the compounds which are more structure-selective than those obtained by collision-induced dissociation or dissociative charge stripping, both procedures in which isomer distinction is based on the behavior of the molecular ions rather than the neutral molecules themselves. All isomers except cis and trans 1,3-pentadiene can be distinguished by their ion/molecule reactions. The conjugated dienes, 1,3-pentadiene and isoprene, form the deprotonated C₁₀H₁₅⁺ dimer which is not generated by 1,4-pentadiene, cyclopentene, or by the allenes, 2,3-pentadiene and 3-methyl-1,2-butadiene. This clear, qualitative difference enables the isomers 1,4- and 1,3-pentadiene to be distinguished, which is otherwise difficult.     

Tetracyanoethylene pi-complex chemistry. Indirect spectrophotometric determination of Diels-Alder-active 1,3-dienes

An indirect spectrophotometric method, based on the rapid Diels-Alder reaction between cisoid 1,3-dienes and tetracyanoethylene (TCNE) and the destruction of an aromatic-TCNE pi-complex, was developed to determine eleven 1,3-dienes in the 0.05-1.00 x 10(-3)M range. These dienes were: cyclopentadiene; 1,3-cyclohexadiene; trans-1,3-pentadiene; 2,4-dimethyl-1,3-pentadiene; trans-2-methyl-1,3-pentadiene; 2-methyl-1,3-butadiene; 9-methylanthracene; 9,10-dimethylanthracene; 1,6-diphenyl-1,3,5-hexatriene; 2,3-dimethyl-1,3-butadiene; and 1,4-diphenyl-1,3-butadiene. Three 1,3-dienes were determined in the 0.05-1 x 10(-4)M range: cyclopentadiene, trans-2-methyl-1,3-pentadiene, and anthracene. The limit of detection for cyclopentadiene in carbon tetrachloride solutions is 0.11 microg/ml. Fourteen 1,3-dienes were found to form stable pi-complexes and could not be determined by the proposed method. For these 1,3-dienes, the spectra of some of the complexes are reported; in addition, relative equilibrium constants for the pi-complexes of 2,5-dimethyl-2,4-hexadiene, cis-1,3-pentadiene, 4-methyl-1,3-pentadiene, and 1,3-cyclo-octadiene were estimated. An explanation of the transient colour in the 1,3-diene-TCNE Diels-Alder reaction is suggested.     

Mutual isomerization of cyclopentyl and 1-Penten-5-y1 radicals

Unimolecular reactions of mutual isomerization of cyclopentyl and 1-penten-5-yl radicals have been investigated by chemical activation. The radicals were generated by adding energized hydrogen atoms (E_H about 23 kcal mol⁻¹) to the double bond of either cyclopentane or 1,4-pentadiene. Based on the extensive steady-state RRKM calculations employing the experimental data from this work as well as from the literature, the threshold energies for the cyclopentyl ring opening and closure are 32 ± 0.3 and 16.2 ± 0.3 kcal mol⁻¹, respectively. The entropy of activation for the ring opening is close to zero.     

Asymmetric radiation-induced inclusion polymerization of 3-methyl-1,4-pentadiene in deoxycholic acid

The radiation-induced polymerization of 3-methyl-1,3-pentadiene (3MPD) as an inclusion complex in deoxycholic acid (DOCA) has produced in good yield the optically active polymer poly(3-methyl-1,4-pentadiene) (P3MPD) whose structure and properties were studied by FT-IR spectroscopy and thermal analysis (TGA, DTG and DTA). The data show that the polymer is essentially trans-1,4-P3MPD as expected for the polymerization in constrained media. Trans-1,4-P3MPD is optically active with [α]_D values comprised between +4.3 and +5.6. The optical rotatory dispersion curve of the P3MPD is completely different from that of DOCA as expected.     

Competitive hydrogenation in binary diene systems on a palladium catalyst

Summary Hydrogenations of individual C₅ dienic substrates (1,3-cyclopentadiene, isoprene, 1,4-pentadiene, cis-1,3-pentadiene, trans-1,3-pentadiene) and their binary mixtures on a heterogeneous palladium catalyst were studied in cyclohexane at 25°C and 2 MPa. Selectivities of the competitive hydrogenations were determined and the substrates relative adsorption coefficients calculated. Effects of the diene structure on their reactivity and the stability of the surface complex are discussed. It was found that differences in selectivity of the competitive hydrogenations of C₅ dienes are caused by the difference both in adsorptivity values and in reactivity of adsorbed molecules. The presence of a five-membered ring in the C₅ dienes leads, , in significant reduction of surface complex stability as compared with acyclic structures of C₅ dienes. On the other hand, it has a very positive effect on the rate of surface reaction.     

Chemoselectivity in 4-methyl-1,3-pentadiene polymerization in the presence of homogeneous Ti-based catalysts

The homogeneous catalyst CpTiCl₃-MAO is able to produce a random copolymer of 4-methyl-1,3-pentadiene with ethylene. ¹³C NMR analysis of the copolymers shows that after insertion of ethylene units, the next 4-ymethyl-1,3-pentadiene unit can be inserted in either 1,2 or 1,4 arrangement. The high chemoselectivity observed in the 1,2-syndiotactic homopolymerization of 4-methyl-1,3-pentadiene with respect to the lower one observed in the copolymerization with ethylene is attributed to a back-biting coordination to the Ti of the active species of the penultimate monomer unit of the growing chain.     

Linear oligomerization of 1,3-pentadiene in presence of catalytic system CoCl2-PPh3-NaBH4

Conclusions The system CoCl₂-PPh₃₂-NaBH₄ catalyzes the oligomerization of trans-1,3-pentadiene to 4-methyl-2,5,7-nonatriene and the 1,3-pentadiene trimer. 4-Methyl-2,5,7-nonatriene is formed predominantly at 95°, while the trimer is the predominant product at 120°. This system does not catalyze the oligomerization of cis-1,3-pentadiene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, 1423–1425, June, 1978.     

Structures of gas phase C5H8 radical cations: A collisional ionization study

Collisional ionization (charge stripping) and charge exchange ionization spectrometry were utilized to determine structures of fourteen cyclic and acyclic C₅H₈ radical cations, including ionized 1,2- 1,3-, 1,4- and 2,3-pentadienes (-PD), isoprene, 1- and 3-methylcyclobutenes (1- and 3-MCB), 3-methyl-1,2-butadiene (3-M-1,2-BD), methenecyclobutane (MECB), cyclopentene, 3-methyl-1-butyne (3-MB), 1- and 2-pentynes and vinylcyclopropane (VCP). The pressure of the charge exchange reagent gas in the ion source was adjusted to generate ions of different energy contents. The structures of the C₅H₈ ions are energy dependent, and their isomerization reactions can be monitored as a function of the amount of internal energy deposited by charge exchange. 1,3-PD, isoprene and cyclopentene radical cations are identified as stable ion structures. 1-MCB, 3-M-1,2-BD and 3-MB radical cations isomerize to isoprene ions, whereas ionized VCP, 3-MCB, 1,2-PD, 2,3-PD, 1,4-PD, 1-pentyne and 2-pentyne ultimately isomerize to the [1,3-PD]⁺˙. Thermodynamic arguments are invoked to corroborate these isomerization reactions. The critical energies of the isomerizations are also estimated.     

Nitropyrazoles: XII. Transformations of the 4-Methyl Group in 1,4-Dimethyl-3,5-dinitropyrazole and Cyclization of the Transformation Products

A preparative procedure for the synthesis of 1,4-dimethyl-3,5-dinitropyrazole by nitration of 1,4-dimethylpyrazole was developed. The reaction of 1,4-dimethyl-3,5-dinitropyrazole with dimethoxymethyl- (dimethyl)amine (N,N-dimethylformamide dimethyl acetal) gave (E)-N,N-dimethyl-2-(1-methyl-3,5-dinitropyrazol- 4-yl)ethenylamine. Acid hydrolysis of the latter afforded (1-methyl-3,5-dinitropyrazol-4-yl)acetaldehyde, and the reaction with sodium nitrite in hydrochloric acid led to formation of 2-hydroxymino-2-(1-methyl- 3,5-dinitropyrazol-4-yl)acetaldehyde. The corresponding O-methyloxime and phenylhydrazone reacted with K₂CO₃ to give 6-methyl-4-nitropyrazolo[4,3-d]isoxazole-3-carbaldehyde O-methyloxime and 1-methyl-3-nitro-4-(2-phenyl-2H-1,2,3-triazol-4-yl)pyrazol-5-ol, respectively. Treatment of (1-methyl-3,5-dinitropyrazol-4-yl)-acetaldehyde with benzenediazonium chloride gave (1-methyl-3,5-dinitropyrazol-4-yl)acetaldehyde phenylhydrazone which underwent intramolecular cyclization with replacement of the 5-nitro group by the action of K₂CO₃ in acetonitrile; in the reaction with K₂CO₃ in ethanol, the 5-nitro group was replaced by ethoxy.     

The preparation of ethyl 7-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-5-methyl-4-oxo-1,8-naphthyridine-3-carboxylate

Ethyl 7-Chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-5-methyl-4-oxo-1,8-naphthyridine-3-carboxylic acid has been prepared by a route involving masking of the C_2,3 double bond through reduction, followed by regioselective deprotonation of the C₅ position and methylation and then regeneration of the C_2,3 double bond via selenation, oxidation, and syn-elimination.     

Selective carbometallation of α,β-unsaturated carbonyl compounds and substituted oxacyclopropanes with zirconium-diene complexes

The reactions of zirconium-dience complexes, ZrCp₂(s-cis-diene), with bifunctional electrophiles, i.e. α,β-unsaturated ketones, unsaturated esters and substituted oxacyclopropanes, were investigated. Reaction of ZrCp₂(s-cis-isoprene) with an equivalent of 3-buten-2-one or alkyl acrylates, selectively gives 1,2-addition products. CC bond formation occured at the C(1) atom of the isoprene moiety whereas 1,3-pentadiene-, 2-methyl-1,3-pentadiene- and 2,4-dimethyl-1,3-pentadiene complexes induced the regioselective 1,2-addition at the C(4) position of the diene moiety. Phenyloxacyclopropane and 2-methyl-3-phenyl-oxacyclopropane also react with ZrCp₂(isoprene) leading to CC bond formation from the C(1) atom of isoprene to the oxirane carbon bearing the phenyl group. The corresponding reactions of 2-methyl-2-butene-1,4-diylmagnesium with α,β-unsaturated carbonyl compounds were also studied and found to give quite different products.     

Synthesis of new carbamate derivatives of indole and their modification

Oximation of indoles having a methoxycarbonylamino group on C⁵ and an acyl group on C³ with hydroxylamine hydrochloride in the presence of pyridine gave the corresponding oximes. The reduction of the 3-C=O group with sodium tetrahydridoborate in the presence of sodium hydroxide was accompanied by removal of the methoxycarbonyl group at the pyrrole nitrogen atom with formation of racemic alcohols. 1,4-Addition of 1-(pyridin-3-yl)butane-1,3-dione to dimethyl 1,4-benzoquinone diimine N,N′-dicarboxylate in dioxane in the presence of sodium methoxide, followed by heating in boiling 22% hydrochloric acid, afforded methyl 2-methyl-5-(methoxycarbonylamino)-3-(pyridin-3-ylcarbonyl)-1H-indole-1-carboxylate. 3-(Dimethylamino)-1-(4-methyl-1,2,5-oxadiazol-3-yl)prop-2-en-1-one reacted with N,N′-bis(methoxycarbonyl)- and N,N′-bis(phenylsulfonyl)-1,4-benzoquinone diimines in methylene chloride and acetic acid, respectively, in the presence of BF₃ · Et₂O to produce indoles having a 1,2,5-oxadiazolylcarbonyl group on C₃.     

Regio- and stereoselective hydrogenation of methyl substituted pentadien-1-ols by baker's yeast

(E)-2-methyl- and (E)-3-methyl-2,4-pentadien-1-ols are reduced to (S)-2-methyl- and (S)-3-methyl-4-penten-1-ols, respectively, using baker's yeast as a regio- and stereoselective reagent. This microbiological conversion provides an efficient route to bifunctional and enantiomerically pure C₆-building blocks containing the C' -CH(Me )-C'' grouping.     

Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro-n-propyl and ethyl radicals revisited

A redetermination of the disproportionation/combination ratio for n–C₃F₇ and C₂H₅ radicals gives a value of Δ(n–C₃F₇, C₂H₅) = 0.13 ± 0.01, independent of the temperature. The radicals were produced by the photolysis of n–C₃F₇COC₂H₅. The previous determinations of this ratio are discussed and are found to be largely incorrect. The values for Δ(CF₃, C₂H₅) and Δ(C₂F₅, C₂H₅) are also re-evaluated, and the recommended values are 0.10 ± 0.02 and 0.12 ± 0.02, respectively. Systems involving perfluoroalkyl and ethyl radicals are complicated due to rapid perfluororadical addition to the ethylene formed in the disproportionation process. The extent of this reaction, and its consequences, are discussed and evaluated. The role of the propionyl (C₂H₅CO) radical in the room temperature photolysis is also assessed. However, it is found that the Δ values determined by the intercept method used in this work are not affected by the secondary reactions that occur. It is concluded that high cross-combination ratios are general to perfluoroalkyl-alkyl radical interactions. For C₃F₇ and C₂H₅ radicals the ratio is 2.7–2.8. Above 100°C ratios exceed 3 due to secondary reactions.     

High pressure isomerization of 1,4-bis(methylthio)hexafluoro-2-butene to-1-butene

The complete bond migration of the internal olefinic bond of trans-1,4-bis(methythio)hexafluoro-2-butene(I) under high pressure to the terminal olefinic bond to form cis- and trans-1,4-bis(methylthio)hexafluoro-1-butene(II) is described. The Teflon-lined high pressure cell maintains a constant pressure at 16,000 atm and 180 to 200°C for 24 hours. The cis- and trans-II are elucidated from gas chromatography-mass spectroscopy, which shows two identical parent ions at m/e value of 255(C₆H₆F₆S₂⁺), but at different elution times. The ¹⁹FNMR data of the isomeric products are summarized. Elemental analysis of II is verified by double focussing high resolution mass spectrometer.     

Kinetics of the reaction between H atoms and allyl radicals

The reaction between H and C₃H₅ has been studied at 291 K. Exciplex laser flash photolysis at 193.3 nm of hexa-1,5-diene-He mixtures generated both H and C₃H₅ ([H] ? [C₃H₅]), which were detected in time-resolved mode by resonance fluorescence and absorption spectroscopy, respectively. Rate coefficients are presented at four pressures in the range 98 ? P/torr ? 400; no clear pressure-dependence is found in this range of pressures and the mean rate coefficient is (2.8 ± 1.0) × 10^?10 cm³ molecule^?1 s^?1. Calculations based on the Troe factorization method confirm that this reaction is near its high-pressure limit under the experimental conditions.     

Fluorescence quenching and laser photolysis of dipyrrolylbenzenes in the presence of chloromethanes

Fluorescence quenching of 1,4-bis(1H-pyrrol-1-yl)benzene, 1-(1H-pyrrol-2-yl)-1-(1-vinyl-1H-pyrrol-1-yl)benzene, and 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene with chloromethanes (methylene chloride, chloroform, and carbon tetrachloride) in solvents with different polarities follows electron-transfer mechanism. The occurrence of an electron-transfer step is confirmed by formation of short-lived pyrrolylbenzene radical cations. An exception is quenching of fluorescence of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene in n-hexane in the presence of CCl₄ and CHCl₃ and in pure CCl₄. In this case, neutral 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene^·-Cl radical is formed via recombination of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene radical cation and chloride anion. A relation was found between the nature of the short-lived species detected by laser photolysis and stable product obtained by stationary photolysis.