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The inclusion of a contact term in the calculation of the paramagnetic shifts induced by Eu(tmhd3) does not Improve the predicted values.  相似文献   

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The Influence of Aniline pK Values on the Formation and Reactivity of Substituted Butadienes from Methyl Coumalate The product of the reaction between 2 equiv. of methyl coumalate ( 1 ) and 1 equiv. of a substituted aromatic amine depends on the pK value of the latter. Aromatic amines with pK values between 1.05 and 2.8 produce bicyclic lactones 4 , whereas those with higher pK values also give 2-azabicyclo[3.3.1]nona-3,7-diene-9-carboxylic acids 9 . The latter, products of the intramolecular Diels-Alder reaction 8 → 9 , may in certain cases even prevail.  相似文献   

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In piperidone-(4)-oximes, the A1,3 strain between the substituent at the exocyclic double bond and a Me group causes the sole formation of anti-isomers. A change of the ring conformation avoids the A1,3 strain in 1-methyl-2,6-diphenyl-3,5-dimethyl-piperidone-(4)-oxime. trans-Configuration of the Me substituents at C-3 and C-5 can be shown in a correspondingly substituted semicarbazone; in this example, the A1,3 strain is avoided by epimerization. This semicarbazone can be transformed into the 3,5-trans-disubstituted piperidone by cerium(IV) oxidation.  相似文献   

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