Smooth conversion of (1) into the S-irnino-1,3-thiazol-2ines ( 3 a ) to (3d) is accomplished in boiling xylene in the presence of isocyanides141. Reaction of (1) with phosphorus pentasulfide without solvent at 140Β°C gives good yields of 3H-1,2.4-dithiazoles (4a) and (4h) which are also accessible from the N-(perfluoroisopropy1idene)carboxamides"' and phosphorus pentasulfidelbI; finally the trapping reaction with norbornene affords the annelated 5,6-dihydro-4H-1,3-thiazines ( S a ) and (Sb).
if (1) is heated to 140Β°C without a trapping reagent it turns yellowish brown but immediately regains its original pale yellow color on cooling.-The reactions mentioned can readily be described in terms of a thermally mobile equilibrium ( 1 ) a 2 ) .
S-Irnino-4,4-his(trijluoromethyl)-l,3-thiazol-2-ines (3)
Equimolar amounts of (I)[*] and isocyanide are refluxed for 12 to 36 h in anhydrous xylene. The residue left on distillation of the solvent crystallizes on rubbing; it is recrystallized from hexane.-The procedure can be applied directly for the preparation of compounds ( 5 ) .
3,3-Bis(trijluo~omethyl)-3H-l,2,4-dithiazoles (4)
Equimolar amounts of ( 1 ) and phosphorus pentasulfide are stirred for 24 h at 140Β°C. Workup is by column chromatography on silica gel (elution with CCIJand subsequent fractional distillation.