1H and 13C NMR spectral study of some 3,5-bis[(E)-thienylmethylene]piperidin-4-ones

Abstract

1H and 13C NMR spectra have been recorded for 3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1a), 3′,3″-dimethyl-3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1b), 5′,5″-dibromo-3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1c), their 1-methyl derivatives 2a– c and 3,5-bis[(E)-thienylmethylene]-2r,6c-diphenylpiperidin-4-one ( 3a). For selected compounds 2D spectra have been recorded. The spectral data are used to study the configuration and conformation of these molecules. The chemical shifts are discussed in light of steric, electronic and magnetic anisotropic effects. The magnetic anisotropic effects of thiophene ring and phenyl group are noteworthy. 1H– 1H COSY spectrum of 2b suggests that long-range 1H– 1H coupling, up to seven bonds, is possible in it. HMBC spectrum of 2b displays the magnetic nonequivalence of C-2 and C-6 and protons at these carbons.