PMR SPECTRA AND cis-trans ISOMERISM OF 2-METHYLENEPYRROLIDINE AND 2-METHYLENETETRAHYDROFURAN DERIVATIVES

Article abstract of DOI:10.1007/BF00568944

A number of secondary enamines and cyclic enol ethers (2-methylenetetrahydrofuran derivatives) were synthesized by the reaction of O-methylbutyrolactim and 2,2-diethoxytetrahydrofuran, respectively, with compounds that have an active methylene link.The absence of reversible cis-trans isomerization was established in a study of the PMR spectra of these compounds.The configuration of the secondary enamines is determined by the possibility of the formation of a strong intramolecular hydrogen bond between the carbonyl-containing substituent and the NH group.In the case of the cyclic enol ethers it was shown that the energy barrier to cis-trans isomerization is greater than 25 kcal/mole and that, as a consequence of this, the geometrical isomers can be separated preparatively.