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61.
Karl Grubmayr Ulrike Gabriella Wagner 《Monatshefte für Chemie / Chemical Monthly》1988,119(6-7):793-812
1H NMR-spectroscopic investigations of the acid catalyzed addition of methanol to dihydrodipyrrinones (Z)-2, (E)-2, and4 show the C-protonation of their enamide parts to be the first and rate determining step forming the key intermediate, the N-acyl-immonium ion N+. Its ability to add nucleophiles diastereoselectively can be used to prepare the adductsl-3 andl-5. Exclusive formation of thelike-isomer can be explained by a stereoelectronically favoured approach of the nucleophile and by the thermodynamically favoured arrangement of the bulky ring substituents. Both explanations are based on low temperature X-ray crystal structure determinations: in the first place, the orientation of the added nucleophile could be found to be nearly parallel to the -plane of the lactam unit and quasi-axial with respect to theenvelope-like conformation of the five-ring lactam; in the second place, the relative orientation of the methoxycarbonyl-metyl-group at C-3 and the pyrrolylmethyl-substituent at C-4 could be found to be atrans-quasi-diequatorial one. 相似文献
62.
Dario MontebugnoliPierfrancesco Bravo Elisabetta BrennaCharles Mioskowski Walter PanzeriFiorenza Viani Alessandro VolonterioAlain Wagner Matteo Zanda 《Tetrahedron》2003,59(36):7147-7156
An effective traceless solid-phase synthesis of chloro-diaminopyrimidines via an amino-de-chlorination reaction of polymer-bound 4-alkoxycarbonylamino-2,6-dichloropyrimidines has been developed. After release from the polymer the target molecules were obtained in good to excellent purity, although with modest regiocontrol. Further reaction of solid-supported N-alkoxycarbonyl-chloro-diaminopyrimidines with secondary amines afforded triaminopyrimidines in good purity under mild conditions, whereas less nucleophilic primary amines did not perform well under the conditions explored so far. 相似文献
63.
64.
A synthetically useful protocol has been developed for the preparation of highly functionalized N-alkenyl-benzimidazol-2-ones. Reaction of commercially available o-phenylenediamines with variously substituted cyclic ketones provides spiro-benzimidazolines. Treatment of these spiro-benzimidazolines with triphosgene in the presence of potassium carbonate results in rapid rearrangement and formation of N-alkenyl-benzimidazol-2-ones in modest to excellent yield for the two-step sequence. Extension of this methodology toward the preparation of a μ opiate receptor antagonist and droperidol, a potent antiemetic and antipsychotic agent, currently a marketed pharmaceutical is also described. Upon treatment of spiro-benzimidazolines with triphosgene in the presence of sodium triacetoxyborohydride, N-alkyl-benzimidazol-2-ones were formed. 相似文献
65.
Boca R Gembický M Herchel R Haase W Jäger L Wagner C Ehrenberg H Fuess H 《Inorganic chemistry》2003,42(22):6965-6967
Triethylenetetramine (L(4)) was used as a tetradentate blocking ligand that, after complexation with Ni(II), leaves two sites ready for ligation with tricyanomethanide. The formed binuclear complex [L(4)Ni(NCC(CN)CN)(2)NiL(4)](ClO(4))(2) exhibits a ferromagnetic coupling with J/hc = +0.15 cm(-1) and g(Ni) = 2.126; below 16 K, a ferromagnetic ordering is evidenced by ac magnetic susceptibility (both in-phase and out-of-phase), magnetization, field-cooled magnetization, and zero-field-cooled magnetization measurements. 相似文献
66.
A rapid and easy route to formamides by microwave assisted N-formylation of primary and secondary amines is described. Using an insoluble polymer or an inorganic solid-supported reagent as a formylating agent, microwave irradiation furnished the corresponding formamides in high yields, with reduced reaction time and solvent volume over the conventional approach. 相似文献
67.
A more consistent, straightforward, and economical protocol for generation of stannylene species and their reaction with BnBr leading to products of O-monobenzylation of diols has been set. It has shown to be specially indicated for substrates bearing vicinal trans 1,2-diol moieties on cyclohexane backbones, which are more resistant to these transformations. Such protocol has been successfully applied to myo-inositol derivatives and acyclic diols. 相似文献
68.
A convenient method has been developed for the synthesis of all mono- and di-O-benzyl ethers of methyl α-L-rhamnopyranoside applying a new stereoselective method for the hydrogenolytic ring-cleavage of benzylidene acetals. Using the prepared dibenzyl ethers as aglycones, the (1→2)-, (1→3)- and (l→4)-linked rhamnosyl-rhamnose derivatives (13–15) were synthesised. Hydrogenolysis of the latter compounds and subsequent acetylation gave the pentaacetates (16–18) of methyl dirhamnosides, which on saponification furnished the free methyl dirhamnosides (19–21). Acetolysis of 16–18 gave the corresponding dirhamnose-hexaacetates which were transformed into the three disaccharides by saponification. The structure of each product was investigated by 13C-NMR spectroscopy, and for the purpose of 13C-NMR studies the mono-O-methyl ethers of methyl α-L-rhamnopyranoside, the diacetates and di-O-benzyl ethers of the latter compounds, and, also the diacetates of methyl α-L-rhamnopyranoside were synthesised.It has been established that, for 13C-NMR investigations of oligosaccharides, the benzyl ethers of monosaccharides are more suitable model compounds than the currently used monosaccharide methyl ethers. 相似文献
69.
Christophe Vande Velde Evi Bultinck Karla Tersago Christian Van Alsenoy Frank Blockhuys 《International journal of quantum chemistry》2007,107(3):670-679
Unhindered ortho‐dimethoxy‐substituted phenyl rings often display a coplanar conformation. A theoretical study of a series of methoxybenzenes consisting of methoxybenzene (anisole), the three dimethoxybenzenes, and 1,2,4,5‐tetramethoxybenzene, at the DFT/B3LYP/6‐311++G** level of theory, allows us to identify the factors influencing the conformational preference and attribute the coplanarity of such methoxy groups to mesomeric effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
70.
The full-length apoprotein (124 kDa) and the chromophore-binding N-terminal half (66 kDa) of the phytochrome of the unicellular green alga Mougeotia scalaris have been heterologously expressed in the methylotrophic yeast Pichia pastoris. Assembly with the tetrapyrrole phycocyanobilin (PCB) yielded absorption maxima (for the full-length protein) at 646 and 720 nm for red- and far-red absorbing forms of phytochrome (Pr and Pfr), respectively, whereas the maxima of the N-terminal 66 kDa domain are slightly blueshifted (639 and 714 nm, Pr and Pfr, respectively). Comparison with an action spectrum reported earlier gives evidence that in Mougeotia, as formerly reported for the green alga Mesotaenium caldariorum, PCB constitutes the genuine chromophore. The full-length protein, when converted into its Pfr form and kept in the dark, reverted rapidly into the Pr form (lifetimes of 1 and 24 min, ambient temperature), whereas the truncated chromopeptide (66 kDa construct) was more stable and converted into Pr with time constants of 18 and 250 min. Also, time-resolved analysis of the light-induced Pfr formation revealed clear differences between both recombinant chromoproteins in the various steps involved. The full-length phytochrome showed slower kinetics in the long milliseconds-to-seconds time domain (with dominant Pfr formation processes of ca 130 and 800 ms), whereas for the truncated phytochrome the major component of Pfr formation had a lifetime of 32 ms. 相似文献