CHARACTERIZATION OF THE CONFORMATIONAL AND TAUTOMERIC PROPERTIES OF BENZYLAMINO DERIVATIVES OF 1,4-DIPHENYL-2-BUTENE-1,4-DIONE USING NMR-SPECTROSCOPY

The H-1 and C-13 NMR chemical shifts of substituted 1,4-dephenyl-2-but ene-1,4-diones indicate that these compounds in CDCl3 solution exist m ainly in the s-trans-s-trans (Z) keto (trans Z) configuration and that hydrogen bonding between the NH proton and the carbonyl group stabili ze this conformer. However, in dmso-d(6) solution, both the s-trans-s- trans (Z) keto (Irans Z) and s-trans-s-cis (Z) keto (cis Z) forms are present with the cis Z form dominating over the trans Z with a ratio o f approximately 4:1. No enol form was detected for these compounds in these solutions. On this bases the presence of the cis keto (E) was el iminated because it is suggested that in going from the trans Z keto t o the cis E keto form, an enol forms will be formed but this was not d etected due to the fact that the rate constant of the trans to cis ket o transformation is very fast. (C) 1997 Elsevier Science B.V.