Geometrical isomers of thione S‐imides

Reaction 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 1 H‐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.