Preparation and Reactions of Thioamides

Thioamides have been prepared from cyanopyrazines with hydrogen sulfide in the presence of base. In this way the following thiocarbamoylpyrazines have been prepared (conditions of reactions) 2-thiocarbamoyl [EtsN/EtOH/HjS (1409) EtjN-pyridine/HjS/lOO (1419) NHj/EtOH/HjS (138)) 2-thiocarbamoylmethyl and its I -ethyl or 1 -phenyl derivatives (Et3N-pyridine/20° or 100°/H2S) (1420, 

1421) 2-amino-3-thiocarbamoyl (triethanolamine/50-55°/12h/H2S) (1212) 2-amino-5,6-diphenyl-3-thiocarbamoyl (triethanolamine/ethanol/H2S/100°/3h) (454) 2-methylamino-6-thiocarbamoyl (triethylamine/EtOH/H2S, fusion with thioacetamide/160°, or P2S5/pyridine/reflux) (945) 2-ethylamino-6-thiocarbamoyl [NH4HS/EtOH (945) Et3N/H2S (992)] 2-diethylamino-6-thiocarbamoyl (EtsN or NH3/EtOH/H2S) (941) 2-(2 -methylpiperidino)-6-thiocarbamoyl (Et3N/EtOH/ H2S) (944) 2-thiocarbamoyl-6-thiomorpholino (Et3N/EtOH/H2S) (943) 2-chloro-6-thiocarbamoyl (EtsN or NH3/EtOH/H2S) (941) and 2-ethyl(propyl or phenyl)thio-6-thiocarbamoyl (EtaN/HjS) (992). 

2-[A -Alkyl(thiocarbamoyl)]pyrazines have also been obtained by heating the 2-(A -alkylcarbamoyl)pyrazine with phosphorus pentasulfide and potassium sulfide in xylene at 100° (1268) and 2-amino-3-carbamoyl-5,6-diphenylpyrazine refluxed with phosphorus pentasulfide in pyridine gave 2-amino-5,6-diphenyl-3-thiocarbamoylpyrazine and the 3-A -butyl(thiocarbamoyl) analogue was prepared similarly (455). 2-Amino-5-chloro-3-(C-imino-C-methylthiomethyl)pyrazine with hydrogen sulfide in pyridine gave 2-amino-5-chloro-3-thiocarbamoylpyrazine (1218). 

2-Methylpyrazine heated with dimethylformamide and sulfur in o-dichloro-benzene at about 150-180° (with and without iodine as catalyst) gave 2-N-methyl(thiocarbamoyl)py razine and 2-A, yV-dimethyl(thiocarbamoyl)pyrazine (1268, 

2-methylpyrazine with methylformamide, sulfur, and iodine at 170-180° gave 2-A -methyl(thiocarbamoyl)pyra2ine (1268), and 2,5-bis-methyl(thio-carbamoyl)pyrazine was prepared similarly (1423). 

---