离子液体BmmimOAc催化2-芳氨基乙醇与二硫化碳一步缩合合成3-芳基-2-噻唑硫酮

噻唑硫酮因具有独特的生物活性，使其在医学和杂环化学等领域有着广泛的应用，从而引起了科研工作者的研究兴趣。本文以离子液体1-丁基-2, 3-二甲基咪唑鎓醋酸盐(BmmimOAc)为催化剂，2-芳氨基乙醇和二硫化碳为起始原料，一步缩合合成3-芳基-2-噻唑硫酮。以2-苯氨基乙醇和二硫化碳的反应为模型，考察了一系列离子液体的催化活性。发现只有阴离子为醋酸根的离子液体才具有催化活性，这可能是由醋酸根的碱性所导致的。在这些阴离子为醋酸根的离子液体中，BmmimOAc的催化活性最高。以其为催化剂，系统考察了反应时间、反应温度、催化剂用量以及二硫化碳和2-苯氨基乙醇摩尔比对该反应的影响。得到最优的反应条件：反应时间6 h、反应温度130 ℃、10%的BmmimOAc用量以及5 : 1的二硫化碳和2-苯氨基乙醇摩尔比。在该反应条件下，目标产物3-苯基-2-噻唑硫酮的收率达到了97%。以不同的2-芳氨基乙醇为原料，考察了该反应的普适性。结果表明无论是具有给电子基团、吸电子基团或较大空间位阻的2-芳氨基乙醇均可顺利地与二硫化碳反应生成相应的3-芳基-2-噻唑硫酮，且分离收率高达83%–95%。核磁共振波谱和质谱分析表明反应过程中BmmimOAc的醋酸根阴离子可以自发地与二硫化碳反应生成硫代醋酸根阴离子，因此离子液体1-丁基-2, 3-二甲基咪唑鎓硫代醋酸盐(BmmimCOS)可能是2-芳氨基乙醇和二硫化碳反应的催化剂。通过核磁共振波谱研究了BmmimCOS与反应底物2-苯氨基乙醇和二硫化碳之间的相互作用，发现BmmimCOS与2-苯氨基乙醇之间存在氢键相互作用。在反应过程中硫代醋酸根阴离子通过氢键作用活化2-苯氨基乙醇，从而促进反应高效进行。基于表征结果，提出了一个可能的反应机理。首先，BmmimOAc自发地与二硫化碳反应生成BmmimCOS。然后，BmmimCOS中的硫代醋酸根阴离子通过氢键作用活化2-苯氨基乙醇。随后，活化的2-苯氨基乙醇与二硫化碳反应生成中间体。最后，中间体分子内环化生成目标产物3-苯基-2-噻唑硫酮。

BmmimOAc-Catalyzed Direct Condensation of 2-(Arylamino) Alcohols to Synthesize 3-Arylthiazolidine-2-thiones

Thiazolidine-2-thiones have attracted much attention because of their unique bioactivity and have been widely used in the fields of medicine and synthetic heterocyclic chemistry. In this work, a simple and convenient route for the synthesis of 3-arylthiazolidine-2-thiones by direct condensation of 2-(arylamino) alcohols with carbon disulfide (CS₂) catalyzed by the ionic liquid 1-butyl-2, 3-dimethylimidazolium acetate (BmmimOAc) has been developed. A series of ionic liquids were used as catalysts in the model reaction of 2-(phenylamino) ethanol with CS₂. The results showed that only the acetate ionic liquids have catalytic activity, perhaps owing to the basicity of the acetate anion. Among these acetate ionic liquids, BmmimOAc showed the highest catalytic activity and was selected as the best catalyst. The effects of reaction time, reaction temperature, amount of BmmimOAc, and CS₂ to 2-(phenylamino) ethanol molar ratio were investigated in detail. The following were found to be the optimal reaction conditions for direct condensation of 2-(phenylamino) ethanol with CS₂: reaction time, 6 h; reaction temperature, 130 ℃; 10% molar fraction of BmmimOAc; and CS₂ to 2-(phenylamino) ethanol molar ratio of 5 : 1. Under these optimized reaction conditions, the product 3-phenylthiazolidine-2-thione was obtained in 97% yield. The reaction scope was explored by investigating the reactions of various 2-(arylamino) alcohols with CS₂. The results showed that the 2-(arylamino) alcohols with electron-donating substituents, electron-withdrawing substituents, or high steric hindrance could be smoothly converted to the corresponding products in excellent isolated yields of 83%–95%. NMR characterizations and mass spectrum indicated that the acetate anion of BmmimOAc could react spontaneously with CS₂ to form the thioacetate anion (CH₃COS^?). Ionic liquid 1-butyl-2, 3-dimethylimidazolium thioacetate (BmmimCOS) might be the actual catalyst in the reaction of 2-(arylamino) alcohols with CS₂. ¹H and ¹³C NMR spectroscopies were used to study the interactions between BmmimCOS and substrates 2-(phenylamino) ethanol and CS₂. The NMR spectra showed the hydrogen bonding interactions between BmmimCOS and 2-(phenylamino) ethanol. The CH₃COS^? anion of BmmimCOS could activate the 2-(phenylamino) ethanol in the catalytic system. Based on the characterization results, a possible reaction mechanism was proposed. Firstly, BmmimOAc reacted spontaneously with CS₂ to form BmmimCOS. Then, CH₃COS^? of BmmimCOS activated 2-(phenylamino) ethanol via hydrogen bonding. Subsequently, CS₂ reacted with the activated 2-(phenylamino) ethanol to form the intermediate. Finally, the intermediate was subjected to intramolecular cyclization to form the final product 3-phenylthiazolidine-2-thione.