Organolithium compounds and 1,3-thiazole-5(4H)-thiones 9 reacted via thiophilic addition on the exocyclic S-atom. The intermediate anion E has been trapped by protonation to give 12 and by alkylation to yield 16, respectively (Schemes 5 and 6). In competition with protonation of E, a fragmentation to benzonitrile and a dithioester 14 was observed (Scheme 5). In some cases, the alkylation of E led to the formation of dithioacetals 17 instead of 16 (Scheme 6). Methyl, ethyl, and isopropyl Grignard reagents and 9 in THF underwent again a thiophilic addition yielding 4,5-dihydro-1,3-thiazoles of type I2 (Scheme 3). In contrast to this result, MeMgI reacted with 9a in Et2O via carbophilic addition to 11. Again a carbophilic attack at C(5) of 9 was observed with allylmagnesium and 2-propynylmagnesium bromide, respectively,in Et2O.