Preparation oftrans- andcis-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines based on the reductivetrans-2,6-dialkylation of pyridine. Synthesis of (±)-epidihydropinidine and (±)-dihydropinidine |
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Authors: | Yu. N. Bubnov E. V. Klimkina A. V. Ignatenko |
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Affiliation: | (1) N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., 117913 Moscow, Russian Federation |
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Abstract: | A general method for the preparation of unsymmetricaltrans-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines6 based on a combination of 1,2-addition of RLi to pyridine andtrans-6-allylation with triallylborane in the presence of methanol was elaborated. It was shown thattrans-piperideines (6 (R=Alk, Ph) isomerize into the correspondingcis-2-allyl-6-alkyl(phenyl)-3-piperideines14 on heating with triallylborane followed by deboronation of aminoborane (16) with methanol and an alkali. The stereochemistry of compounds6 and14 was determined by two-dimensional NOE spectroscopy. A possible mechanism of the formation oftrans-amines6 and their transformation intocis-isomers14 is discussed. Alkaloids (±)-epidihydropinidine (trans-2-methyl-6-propylpiperidine2a, 70%) and (±)-dihydropinidine (cis-2-methyl-6-propylpiperidine1d, 71%) were synthesized by hydrogenation of compound6a (R=Me) and14a (R=Me), respectively, over Raney nickel. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 467–474, March, 1998. |
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Keywords: | allylboration pyridine, 1,2-addition, alkyl(aryl)lithium, triallylborane trans- andcis-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines trans-cis-isomerization stereochemistry piperidine alkaloids (±)-epidihydropinidine (±)-dihydropinidine |
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