Synthesis of Schiff Bases from Substitute Aromatic Aldehydes and 2-(4-aminophenyl)acetonitrile Catalysed by 3,5-difluoroarylboronic Acid

Abstract

A simple efficient method for synthesis of Schiff bases in good yields from aromatic aldehydes and 2-(4-aminophenyl)acetonitrile catalysed by 3,5-difluoroarylboric acid at room temperature for 2 hours is reported.Keywords: Schiff bases, 3,5-difluoroaryllboronic acid, aromatic aldehydes, 2-(4-aminophenyl) acetonitrileIn recent years, the synthesis of Schiff base compounds has attracted much interest among organic chemists. Schiff bases have played a very important role in medical biology, 1,2 functional materials, 3 catalysis chemistry 4 and coordination chemistry 5 in the few past decades, especially in asymmetric catalytic reactions. Schiff bases are frequently used as ligands in some organic synthesis reactions such as asymmetric sulfoxidation, 6 Suzuki-Miyaura 7 and enantioselective Henry reaction 8 (Fig. 1). These reactions catalysed by chiral Schiff bases provided high ee values. In the past, various catalysts such as TiO 2 , 9 MgSO 4 , 10,11 NbCl 5 , 12 Pt, 13 ionic liquids, 14 CaO, 15 molecular sieves, 16 clay, 17 P 2 O 5 /SiO 2 , 18 P 2 O 5 /Al 2 O 3 , 19 dioxane/ AcOH 20 and boric acid 21 were successfully used to synthesise Schiff bases. At the same time, some other reaction techniques appeared, for instance, ultrasound irradiation 22 , microwave irradiation 23,24 and solvent-free reaction 25 . However, syntheses of Schiff bases usually suffer from high reaction temperatures, long reaction times and low yields. Therefore, improvement of these reactions is required.To our knowledge, boronic acid, ferrocenic boronic acid or substituted arylboronic acids have not been studied as catalysts for the synthesis of Schiff bases. In this paper, we report our research on substituted arylboronic acids as catalysts for the synthesis of Schiff bases. We found that 3,5-difluoroarylboric acid was an efficient catalyst for the synthesis of Schiff bases. Under mild conditions, 18 new compounds were synthesised. Key