J. Bosch, M. Rubiralta
May 1, 1981
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Journal
Journal of Heterocyclic Chemistry
Abstract
cis-2-Aryl-3-isopropenyl-1,3-dimethylpyrrolidines Ha and IIb have been synthesized by an unambiguous way, thus confirming the structure of the methylene derivatives obtained as by-products in the Stevens rearrangement of 1-benzyl-1,3,4-trimethyl-1,2,5,6-tetrahydropyridinium salts Ia and Ib. The synthesis is based on the acid-induced intramolecular cyclization between an iminium salt and the α-position of a ketal group. Thus, condensation between amino ketal XXI, prepared via Gabriel synthesis from 5-chloro-3-methyl-2-pentanone, and the appropriate aldehyde afforded imines XXI. Their treatment with dry hydrogen chloride followed by acid hydrolysis and methylation gave 3-acetylpyrrolidines IV, which were transformed into the isopropenyl derivatives II by reaction with methyl-lithium and further dehydration.