Novel stereoselective synthesis of (E)-cinnamonitriles via Heck arylation of acrylonitrile catalysed by a silica-supported bidentate arsine palladium(0) complex

Abstract

Cinnamonitriles are important synthetic intermediates and many methods can be used for the synthesis of cinnamonitriles, such as the reaction of cinnamaldehydes with dimethylsulfur diimides, 1 Wittig-Horner reaction of (EtO) 2 POCH 2 CN with aldehydes 2 and the treatment of acid chlorides with sulfonamides. 3 In recent years, more attention has been given to the stereoselective synthesis of (E) and (Z)-cinnamonitriles. Huang et al. 4 reported that (Z)-cinnamonitriles were prepared in 78-98% yields by the desulfonylation of α-phenylsulfonylcinnamonitriles in the presence of NaHTe. Guo and Zhang 5 found that (E)-cinnamonitriles could be obtained in 68-85% yields by a procedure of reduction of α-phenylsulfonylcinnamonitriles with SmI 2 in THF-MeOH solution. Although these methods have provided useful routes for stereoselective synthesis of (E) and (Z)-cinnamonitriles, sometimes the α-phenylsulfonylcinnamonitriles are not readily available. A convenient alternative technical synthesis of (E)-cinnamonitriles is the Heck arylation of aryl iodides with acrylonitrile, the homogeneous palladium complexes such as [Pd(OAc) 2 ] or [PdCl 2 (PPh 3 ) 2 ] are usually used as the catalysts in the arylation reaction. 6,7 The amount of catalyst used is about 1 mol% of reactant; however, use of homogeneous palladium catalysts is still uneconomic for large-scale preparation in the laboratory and for industrial production. As Heck 8 has noted, practical application of the reaction under such conditions is not feasible due to its expense. Polymer-bound organotransition metal complexes having high activity and selectivity offer several significant advantages in synthetic and industrial chemistry; among these, the ease of separation of the catalyst from the desired reaction products and the ease of recovery and reuse of the catalyst are most important. Recently, we have found that the silica-supported bidentate arsine palladium(0) complex ['Si'-2As-Pd(0)] is a highly active catalyst for Heck arylation of styrene and acrylic acid with aryl iodides. 9 Herein we wish to report that (E)-cinnamonitriles can be synthesised stereoselectively via Heck arylation of acrylonitrile with aryl iodides catalysed by a silica-supported bidentate arsine palladium(0) complex (Scheme 1).Treatment of iodobenzene (2 mmol) with acrylonitrile (4 mmol) in p-xylene (0.3 ml) at 90°C for 6 h in the presence of 'Si'-2As-Pd(0) (0.01 mmol), and Bu 3 N (2.2 mmol) afforded (E)-cinnamonitrile in 89% yield. When [Pd(OAc) 2 ] (0.01 mmol) was used as the catalyst, (E)-cinnamonitrile was obtained in 78% yield under same conditions. We applied the reaction to various substituted iodobenzenes, typical results are summarised in Table 1. As seen from the Table 1, the arylation reactions of acrylonitrile with substituted iodobenzenes also proceeded smoothly and a variety of substituted (E)-cinnamonitriles were obtained in high yields. The arylation reaction can tolerate a variety of functional