Geometrical isomers of thione S‐imides

Abstract

AbstractReaction of highly substituted dithiobenzoates 1 (a‐e) with chloramine‐T in methanol at 20°C gives, in high yields, thione S‐imides 2 (a‐e) to which the E‐geometry was assigned. Heating of these compounds in methanol for 1 hr causes thermodynamic isomerization to the Z‐isomers 3 (a‐e). Similarly, 2,4,6‐trimethyl‐thiobenzophenone gives the corresponding E‐ and Z‐S‐tosylimides 6 and 7. Irradiation of thione S‐imides 2, 3, 6 and 7 leads to extrusion of sulfur yielding N‐tosylimines 4 and 8. The geometrical configurations were based on ASIS experiments. From the 1H‐NMR spectra of 2 and 3 the preferred conformation of the thione S‐imides have been deduced (S‐trans conformation for the E‐isomer 2 and a folded S‐cis conformation for the Z‐isomer 3). It will be shown that in order to obtain stable thione S‐tosylimides from dithiobenzoates and thiobenzophenones, steric hindrance in the direct environment of the thiono function is a prerequisite.