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1991 (3)
1Author    EnriqueG. Utiérrez-PueblaRequires cookie*
 Title      
  Reference    Z. Naturforsch. 46b, 1113 (1991); eingegangen am 9. Januar 1991 
  Published    1991 
  Keywords    Hexachlorodicuprates, Tetrachlorocuprates, 3-D iethylam ino-5-phenyl-1, 2, 4-dithiazolium Salts, Synthesis, Crystal Structure 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-1113_n.pdf 
 Identifier    ZNB-1991-46b-1113_n 
 Volume    46 
2Author    HansM. Öhrlea, K. Arin Bluhme-Hensena, BirgitM. Iddelhauveb, DietrichM. Ootzb, H. Artm, W. Underlich15Requires cookie*
 Title    Cyclisierung von Amidoximen mit Oxybis(diphenylboran) Cyclization of Amidoximes with Oxybis(diphenylborane)  
  Reference    Z. Naturforsch. 46b, 1219—1222 (1991); eingegangen am 2. April 1991 
  Published    1991 
  Keywords    Am idoxim es, 2, 3-D ihydro-l, 3, 5, 2-oxadiazaborol Derivatives, Crystal Structure 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-1219.pdf 
 Identifier    ZNB-1991-46b-1219 
 Volume    46 
3Author    Ulrike Holzgrabe, Willy Friedrichsen, Rl-FH. EsseRequires cookie*
 Title    Keto-Enol-Tautomerism and Configurational Isomerism of 2,6-Disubstituted 4-Piperidone-3,5-dicarboxylates [1]  
 Abstract    The dialkyl 2,6-dialkylsubstituted 4-piperidone-3,5-dicarboxylates were synthesized by a M annich procedure. Depending on the substitution at the nitrogen keto-enol-tautomerism and a configurational isomerism at C 2 is observed. The structure o f the N-substituted piperi-done 24 E (C 18H 29N 0 5) has been determined by X-ray analysis: it is characterized by an enol structure o f the /?-ketoester and an axial position o f the alkyl group at C 2 and an equatorial one o f the alkyl group at C 6. The O -H -O hydrogen bond shows characteristic values o f a strong hydrogen bond. The N-unsubstituted piperidones adopt a ketone structure with the all-equatorial position o f all substituents. This stereochemistry is confirmed for other enolic and ketone analogues by N M R spectroscopic methods. To work out the reason for the different thermodynamic stabilities o f the different stereochemical structures o f N-substituted and N-unsubstituted piperidones, various semiempirical calculations were done for series o f simple pairs o f carbonyl/enol tautomers, substituted acetoacetates, oxoglutarate as well as o f syste­ matically varied substituted cyclohexanone, 4-oxacyclohexanone and 4-piperidone deriva­ tives. 
  Reference    Z. Naturforsch. 46b, 1237—1250 (1991); received Novem ber 2 1990 
  Published    1991 
  Keywords    2, 6-Disubstituted 4-Piperidone-3, 5-dicarboxylates, High-resolution N M R, X-Ray, Theoretical Calculations 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-1237.pdf 
 Identifier    ZNB-1991-46b-1237 
 Volume    46