A series of monothioimides and dithioimides were synthesised using Lawesson
's reagent. It has been found that two main effects affect thionation react
ion. The high polarity of carbonyl groups leads to good yields of mono- and
dithioimides. On the other hand, steric hindrance in the vicinity of the c
arbonyl group strongly inhibits the replacement of the oxygen atom by sulfu
r.