Preparation of 1,3-dienyl organotrifluoroborates and their Diels–Alder/cross-coupling reactions

Abstract 2-BF 3 -substituted 1,3-butadienes with potassium and tetrabutyl ammonium counterions have been prepared in gram quantities from chloroprene via a simple synthetic procedure. The potassium salt of this new main group element substituted diene has been characterized by 1 H, 13 C, 11 B, and 19 F NMR and the tetra n -butyl ammonium salt was also characterized by X-ray crystallography. Diels–Alder reactions of these dienes with dienophiles such as ethyl acrylate, methyl vinyl ketone, and N -phenylmaleimide are reported as well as subsequent Pd-catalyzed cross-coupling reactions of those Diels–Alder adducts. 4-Phenyl-2-BF 3 -substituted 1,3-diene was prepared by magnesium–halogen exchange from the corresponding 2-bromo and iodo dienes. The 4-phenyl-2-bromo-1,3-butadiene was also characterized by X-ray crystallography. 4-Phenyl-2-BF 3 -1,3-butadiene was used in Diels–Alder/cross-coupling reactions and the product of a Diels–Alder reaction with N -phenylmaleimide followed by cross-coupling with 4-bromo-benzonitrile was also characterized by X-ray crystallography.