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181.
The Mannich reaction between selectively tetratosylated resorcin[4]arene, formaldehyde and (S)-phenylalanine (or (S)-phenylglycine) methylamide gave cyclochiral mono- or dibenzoxazines with high diastereoselection as revealed by NMR and X-ray structural studies. X-ray structures of the products show the variety of intramolecular interactions that can be responsible for the diastereoselection of this acid-catalyzed reaction. 相似文献
182.
1-Alkyl imidazoles react smoothly with dialkyl acetylenedicarboxylates in the presence of pyridine carboxaldehydes to diastereoselectively produce 1,8a-dihydro-7H-imidazo[2,1-b][1,3]oxazine derivatives in excellent yields. 相似文献
183.
Pedro Bernal Sherril D. Christian Edwin E. Tucker 《Journal of solution chemistry》1986,15(11):947-956
An automated vapor pressure apparatus has been used to obtain measurements of the vapor pressure of aqueous solutions of fluorobenzene at temperatures of 15, 25, 35, and 45°C, and in the concentration range 0 to 0.011M. The results have been interpreted to infer the dimerization constant of fluorobenzene in very dilute aqueous solutions, equivalent to the second virial coefficient of interaction between fluorobenzene molecules. The hydrophobic association of fluorobenzene molecules is thermodynamically quite similar to that of benzene at comparable temperatures and concentrations. A dimerization constant of fluorobenzene of 0.56 M–1 at 30°C and an endothermic enthalpy of association equal to 3.9 kcal-mol–1 are calculated from the measurements. 相似文献
184.
A. A. Koridze Y. I. Zdanovich N. V. Andrievskaya Yu. Siromakhova P. V. Petrovskii M. G. Ezernitskaya F. M. Dolgushin A. I. Yanovsky Yu. T. Struchkov 《Russian Chemical Bulletin》1996,45(5):1200-1206
Diyne FcCmCC.CFc (Fc is ferrocenyl) reacts with Ru3(CO)12 in boiling hexane to yield binuclear complexes Ru2 and Ru2(CO)6(C4Fc2(C=CFc)2C=O) containing ruthenacyclopentadiene and diruthenacycloheptadienone rings, respectively. The isomerism of the complexes is due to the different ways of coupling of the alkyne fragments of the diyne, namely, head-to-head, head-to-tail or tail-to-tail. The reaction of enyne PhC=CCH=CHPh with Ru3(CO)12 under similar conditions gives isomeric binuclear complexes Ru2(CO)6(C4Ph2(CH=CHPh)2) and trinuclear clusters Ru3(CO)6(w-CO)2(C4Ph2(CH=CHPh)2) and Ru3(CO)8(3-,1-1-4-2 C4Ph2(CH=CHPh)2). The structure of the latter was determined by X-ray diffraction analysis. The Ru3 triangle coordinates eight terminal CO groups and the organic ligand resulting from the head-to-head dimerization of enyne molecules; the ruthenacyclopentadiene moiety is 4-coordinated to the Ru(CO)2 group, and the third ruthenium atom is 2-bound to one of the PhCH=CH groups.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1261–1267, May, 1996. 相似文献
185.
Zhi Hua MA Cong LIU Yong Hua ZHAO Wei LI Jian Bo WANG* Key Laboratory of Bioorganic Chemistry Molecular Engineering of Ministry of Education Department of Chemical Biology College of Chemistry Peking University Beijing 《中国化学快报》2002,13(8)
b-Amino acids and their derivatives have attracted considerable attention in recent years due to their occurrence in biologically active natural products, such as dolastatins 11, cyclohexylnorstatine 22 and taxol 33. bAmino acids also find application in the synthesis of blactams4, piperidines5, indolizidines6. Moreover, the peptides consisting of bamino acids, the so called bpeptides, have been extensively studied recently7. Consequently, considerable efforts have been directed to the synt… 相似文献
186.
The diastereoselective cyanation of α‐keto amides using trimethylsilyl cyanide in the presence of a Lewis acid is described. The corresponding O‐acetylated cyanohydrins are obtained in good to high levels of stereoselectivities. The predominance of products with the S absolute configuration at the newly generated stereogenic center was deduced from single crystal X‐ray analysis. 13C NMR data suggest that a preferential s‐cis conformation was formed by the chelation of a Lewis acid to the dicarbonyl oxygen atoms. 相似文献
187.
The properties of six dihydrogen-bonded (DHB) dimers with the BeH2 molecule as a proton acceptor were calculated by MP2, CCSD(T) and B3LYP methods. The structural, energetic and spectroscopic parameters are presented and analyzed in terms of their possible correlation with the interaction energy and the intermolecular H...H separation. The symmetry-adapted perturbation theory (SAPT) calculations were performed to gain more insight into the nature of the H...H interactions. The studied complexes are divided into three groups based on the calculated intermolecular distances and the interaction energies which range from approximately -1 to -42 kJ mol(-1). The analysis of the interaction energy components indicates that, in contrast to conventional hydrogen bonds, the induction energy is the most important term in the BeH2NH4+ complex. On the other hand, there is no sharp boundary between the DHB complexes classified as hydrogen bonded and van der Waals systems. The complexation-induced changes in vibrational frequencies and in proton shielding constants show a relationship with the interaction energy. The values of the 2hJXH and 3hJBeX coupling constants correlate well with the interaction energy and with the intermolecular distance. 相似文献
188.
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Inside Back Cover: New Insights into the Hexaphenylethane Riddle: Formation of an α,o‐Dimer (Angew. Chem. Int. Ed. 13/2015) 下载免费PDF全文