Novel Catalyst-Free Synthesis of Some 3-Alkylaminoquinoxaline-2(1H)-thiones and 3-Alkyloxyquinoxaline-2(1H)-thiones in Ethanol.

Seventeen 3-alkylaminoquinoxaline-2(1H)-thiones and 3-alkyloxyquinoxaline-2(1H)-thiones were prepared by a novel thionation protocol from the readily available quinoxaline-2,3-dione in excellent overall yields. This protocol starts with the chlorination of dione using thionyl chloride to give 2,3-dichloroquinoxaline followed by the reaction with equimolar amounts of N-nucleophiles (primary amines and secondary amines) or O-nucleophiles (phenols and alcohols) to principally afford 2-alkanamino-3-chloroquinoxalines or 2-alkyloxy-3-chloroquinoxalines, respectively. The chloroquinoxalines reacted with the thionation reagent N-cyclohexyl dithiocarbamate cyclohexyl ammonium salt in ethanol under reflux to principally give the corresponding quinoxalin-2-yl cyclohexylcarbamodithioate that finally rearranges in situ to give the corresponding thiones in 76-93% overall yields. Our novel catalyst-free synthesis of some 3-alkylaminoquinoxaline-2(1H)-thiones and 3-alkyloxyquinoxaline-2(1H)-thiones in ethanol protocol has many advantages compared with traditional methods: excellent yields, one-pot reaction, simple experimental procedure, and commercial availability of the required reagents. In addition, this method could be generalized to involve a wide range of amines, phenols, and alcohols, and also during the reaction, we did not notice a bad odor. The structures of synthesized compounds are elucidated via different methods such as 1H NMR, 13C NMR, elemental analysis, and MS.