Ionic liquid Mediated Synthesis of Schiff bases bearing thiazole and indole moieties.

AIMS Ionic liquid Mediated Synthesis of Schiff bases bearing thiazole and indole moieties. BACKGROUND Synthesis of biologically active heterocyclic compounds using environmentally benign method. MATERIALS AND METHODS A mixture of amino thiazoles (3a-i) (20 mmol), indole-3-carboxyaldehyde (4) (20 mmol) and ionic liquid (80 mmol) was stirred in ethanol (30 mL) at r.t. The progress of the reaction was monitored by thin layer chromatography. After stirring the reaction mass for 2h the solid mass appeared in the reaction was filtered and crystalized using ethanol. The melting points and the yields of the derivatives are recorded in the Table 2. The filtrate was distilled and residue, ionic liquid was reused for the further reactions of the same batch and noted that it gave moderate to good yields of the products. RESULTS AND DISCUSSION Thus a convenient synthetic protocol for the synthesis of new Schiff bases, N-(4-(3-(4-(4- phenylthiazol-2-ylimino) methyl) phenoxy) propoxy) benzylidene)-4-phenylthiazol-2-amines, (8a-i) and N-((1H-indol-3-yl) methylene)-4-phenylthiazol-2-amines,(5a-i) has been developed by separately allowing the interactions of bis aldehyde (7) and 3-formyl indole (4) with amino thiazoles, (3a-i) in 2-hydroxy ethyl ammonium acetate, an ionic liquid, at r. t. (Scheme 1). Acetophenones, (1a-i) and thiourea were allowed to condense in PEG-400 in the presence of NBS and obtained better yields of aminothiazoles, (3a-i). Amino thiazoles when separately condensed with indole-3-carboxyaldehyde (4) and bis aldehyde (7) in ionic liquid, 2-hydroxy ethyl ammonium acetate (9) gave respective new azomethines, N-((1H-indol-3-yl) methylene)-4-phenylthiazol-2-amines, (5a-i) and N-(4-(3-(4-(4-phenylthiazol-2-ylimino) methyl) phenoxy) propoxy) benzylidene)-4-phenylthiazol-2-amine, (8a-i), respectively. CONCLUSION We have synthesized new Schiff bases at r.t. using freshly prepared ionic liquid as medium. This method useful for the preparation of library of Schiff bases. The starting, material required for the synthesis of the Schiff bases, amino thiazoles have been prepared using green reaction media.