Simple syntheses of 4,4-disubstituted 2-thiazolin-5-thiones, which have so far been difficult to obtain, are described. These compounds are stable and undergo a number of different reactions. The first type of reaction discussed here are cyclosubstitutions, which occur on heating in the presence of electron-deficient acetylenes. 1,3-Dithiafulvenes are thus formed via nitrile elimination. Thiazolinthiones show different chemical behavior in reactions with ynamines. On warming, thiazolinylidene-thioamides and -thioketones are formed via a [2+2] cycloaddition, followed by an electrocyclic ring opening reaction. The third reaction type has been observed in the conversion with 1,3-dipolar reagents. In situ generated benzonitriliumbetaines undergo 1,3-dipolar cycloaddition to the exocyclic C,S-double bond and form dithiaspiro[4.4]nonadienes.