Synthesis of Vinyl Isocyanides and Development of a Convertible Isonitrile
The reaction of isocyanomethylenetriphenylphosphorane, generated in situ from the corresponding phosphonium salt, with a diverse set of aldehydes afforded vinyl isocyanides in good to high yields. Excellent E-selectivity was observed for aliphatic aldehydes and 2,6-disubstituted aromatic aldehydes, whereas Z-olefins were formed predominantly with ortho-substituted aryl aldehydes. (Z)-1-Bromo-2-(2-isocyanovinyl)benzene (5l) was found to be a truly universal isonitrile since, after Ugi reaction, the resulting secondary amide unit (RNHCO−) is convertible under both acidic and basic conditions. The application of 5l in the synthesis of polyheterocycles is also illustrated.