Base-catalyzed Formation of Enamines from β,β-Dicyanostyrene Derivatives with N-Bromosaccharin
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A new method for the synthesis of functional enamines from β,β-dicyanostyrene derivatives and N-bromosaccharin(NBSA) was developed. In the presence of Na2CO3, the the reaction of β,β-dicyanostyrene derivatives with NBSA can generate the corresponding enamines smoothly in a mixed solvent of dichloromethane and N,N-dimethylformamide(DMF)(volume ratio 1:1) at 50 °C. The reaction of 14 kinds of β,β-dicyanostyrene derivatives with NBSA was investigated. Screened olefins afforded the corresponding enamines in good to excellent yields(up to 94%), indicating that the method has a wide adaptability for the substrate. The catalyst used is inexpensive and stable for storage. The amino groups of all products in their structures are on the α-position of products, revealing the reaction has an excellent regioselectivity. The possible pathway involving aminobromination of β,β-dicyanostyrene derivative with NBSA first and then elimination of HBr process in one pot has been proposed. The structures of all products were confirmed by 1H NMR, 13C NMR and HRMS analysis.
Keywordsβ,β-Dicyanostyrene derivative Functional enamine Sodium carbonate N-Bromosaccharin
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