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141.
Andrea Schfer Manfred Hesse Max Viscontini Henning Paul Berthold Fischer 《Helvetica chimica acta》1995,78(7):1763-1776
The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one ( 1a ) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4 ) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L -biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c . 相似文献
142.
Phase-transfer alkylation of the 2-oxocycloalkane-l-carbonitriles 1a and 1b with ethyl 4-bromo-3-methoxy-2-butenoate ( 2 ), followed by deprotection and base-catalyzed cyclization gave the annulated cyclopentenones 5a and 5b , respectively, in high overall yields (Scheme 1). Stereoselective catalytic hydrogenation of 5b followed by de-ethoxycarbonylation afforded 14-oxo-cis-bicyclo[10.3.0]pentadecane-l-carbonitrile ( 7 ). Treatment of 7 with LiN(i-Pr)2 in THF gave the known synthetic muscone precursor 8 (Scheme 2). The tricyclo[10.4.0.01,15]hexadecan-14-one ( 14 ) was prepared from 7 in 5 steps by a reaction sequence proceeding without affecting the chiral centres (Scheme 2). The structure of 14 was established by X-ray structure analysis (Figure). 相似文献
143.
The title complexes, the Re(O)L(2)(Solv)(+) complexes (L = hoz, 2-(2'-hydroxyphenyl)-2-oxazoline(-) or thoz, 2-(2'-hydroxyphenyl)-2-thiazoline(-); Solv = H(2)O or CH(3)CN), are effective catalysts for the following fundamental oxo transfer reaction between closed shell molecules: XO + Y --> X + YO. Among suitable oxygen acceptors (Y's) are organic thioethers and phosphines, and among suitable oxo donors (XO's) are pyridine N-oxide (PyO), t-BuOOH, and inorganic oxyanions. One of the remarkable features of these catalysts is their high kinetic competency in effecting perchlorate reduction by pure atom transfer. Oxo transfer to rhenium(V) proceeds cleanly to afford the cationic dioxorhenium(VII) complex Re(O)(2)L(2)(+) in a two-step mechanism, rapid substrate (XO) coordination to give the precursor adduct cis-Re(V)(O)(OX)L(2)(+) followed by oxygen atom transfer (OAT) as the rate determining step. Electronic variations with PyO derivatives demonstrated that electron-withdrawing substituents accelerate the rate of Re(VII)(O)(2)L(2)(+) formation from the precursor adduct cis-Re(V)(O)(OX)L(2)(+). The activation parameters for OAT with picoline N-oxide and chlorate have been measured; the entropic barrier to oxo transfer is essentially zero. The potential energy surface for the reaction of Re(O)(hoz)(2)(OH(2))(+) with PyO was defined, and all pertinent intermediates and transition states along the reaction pathway were located by density functional theory (DFT) calculations (B3LYP/6-31G). In the second half of the catalytic cycle, Re(O)(2)L(2)(+) reacts with oxygen acceptors (Y's) in second-order reactions with associative transition states. The rate of OAT to substrates spans a remarkable range of 0.1-10(6) L mol(-)(1) s(-)(1), and the substrate reactivity order is Ph(3)P > dialkyl sulfides > alkyl aryl sulfides > Ph(2)S approximately DMSO, which demonstrates electrophilic oxo transfer. Competing deactivation and inhibitory pathways as well as their relevant kinetics are also reported. 相似文献
144.
Marita Hohmann Luise Krauth-Siegel K. Weidenhammer Wolfgang Schulze Manfred L. Ziegler 《无机化学与普通化学杂志》1981,481(10):95-106
Molecular and Crystal Structures of (CO)4W(μ-S-t-C4H9)2W(CO)4, η7-C7H7W(μ-SC6H4CH3)3W(CO)3 and η7-C7H7W(μ-S-n-C4H9)3W(CO)(μ-S-n-C4H9)2W(CO)4 The molecular structures of the two binuclear complexes (CO)4W(μ-S-t-C4H9)2W(CO)4 and η7-C7H7W(μ-SC6H4CH3)3W(CO)3 and of the tungsten cluster η7-C7H7W(μ-S-n-C4H9)3W(CO)-(μ-S-n-C4H9)2W(CO)4 respectively are described. In the nonlinear trinuclear cluster the central tungsten atom is connected to the two tungsten atoms by two and three μ-S-n-C4H9 bridges respectively and additionally by one W? W bond each. The coordination sphere of the W atoms is completed by a η7-C7H7 ring and four CO groups respectively; the central tungsten carries an additional CO group. 相似文献
145.
(Z)-2-Butenyl-dimethoxyborane adds smoothly to propanal and benzaldehyde to afford the homoallyl alcohols (R*,R*)- 1 and (R*,R*)- 2 , In contrast (E)-2-butenyl-dimethoxyborane leads to adducts having the (R*,S*)-configuration. Dimethoxy-(Z)-2-pentenylborane, dimethoxy-(Z)-(2-methyl-2-butenyl)borane and (2Z,4E)-or (2E,4Z)hexadienyl-dimethoxyborane, treated with propanal, give (R*,R*)- 3 , (R*,R*)- 4 , (E),(R*,S*)- 5 and (Z),(R*, R*)- 5 , respectively. A transition state model implying a pericyclic electron motion is in perfect agreement with the regio- and stereoselective outcome of these borane reactions. 相似文献
146.
Ring Enlargement by Lactonization of Methylated 1-(3′-Hydroxypropy1)-2-oxocyclododecane-1-carbonitriles The title compounds were prepared by Michael reaction of 2-oxocyclododecane-1-carbonitrile ( 1 ) and acrylaldehyde and its derivatives followed by NaBH4 reduction or methylation of the aldehyde group with [(CH3)2Ti(i-PrO)2] (Scheme 1). In all cases, the ring enlargement was performed with Bu4NF/THF to give different methylated derivatives of 12-cyano-15-pentadecanolide ( 13 ) in 95–99% yield. The Yields of the rearrangement products are not dependent on the positions and numbers of the CH3 groups in the side chain of 3 . The lactonization reaction is of unremarkable stereoselectivity. 相似文献
147.
Manfred Schlosser 《Angewandte Chemie (International ed. in English)》1974,13(11):701-706
Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis. 相似文献
148.
During the examination of extracts from Oncinotis tenuiloba STAPF a new polyamine, N4-benzoylsperimidine ( 8 ), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative 13 , and the three possible N-benzoyl-substituted isomers of spermidine 5, 8 , and 11 together with their peracetylated derivatives 12–14 , respectively, were synthesized and identified. 相似文献
149.
A bidentate ligand consisting of a 2-(diphenylphosphinoethyl)-thio moiety was attached to β-cyclodextrin at the 6-position. The corresponding norbornadiene Rh(I) complex in the form of the BF4− salt was prepared. 相似文献
150.
Wolfgang A. Herrmann Ricardo Serrano Adolf Schäfer Ulrich Küsthardt Manfred L. Ziegler Ernst Guggolz 《Journal of organometallic chemistry》1984,272(1):55-71
Short-wavelength photolysis of tricarbonyl(η5-pentamethylcyclopentadienyl)rhenium (1) (λ < 300 nm, quartz-glass) in tetrahydrofuran yields under partial or complete decarbonylation three novel organorhenium compounds, with the relative yields depending upon the irradiation time. Formed by exhaustive oxidative decarbonylation, the complex trioxo(η5-pentamethylcyclopentadienyl)rhenium(VII) (5) represents the first example of the new class of oxo half-sandwich complexes. The derivatives (μ-O)[(η5-C5Me5)Re(CO)2]2 (2; Me = CH3) and (η5-C5Me5)2Re2(CO)2O2 (3; Me = CH3) containing both oxo and carbonyl ligands are formed from 1 at shorter irradiation times. Both compounds are isolable intermediates along the mechanistically not yet fully established sequence 1 → → 5 as they are degraded to 5 under CO2 elimination in the presence of air and/or light. The mixed oxo carbonyl complex 2 has been characterized by means of single-crystal X-ray diffraction techniques (triclinic, space group P-Ci1; a 907.4(2), b 1040.2(3), c 1414.3(4) pm; α 79.99(2), β 88.42(2), γ 66.18(2)°; Riso = 0.068, Raniso = 0.037, Rw = 0.031). The molecular structure centres around an isosceles Re2O triangle whose metal centres exhibit a strongly distorted square-pyramidal geometry; the metal-metal distance recorded at 281.7(1) pm is in agreement with a single bond by the EAN rule. The centrically coordinated, planar five-membered ring ligands are parallel to each other (interplanar angle 2°) and occupy trans-positions with respect to the central Re2O geometry. 相似文献