Palladium-Catalyzed Cross-Coupling of (2-Ethoxyvinyl)boranes with Aryl and Benzyl Halides. A New Method for Conversion of Organic Halides into Aldehydes with Two More Carbon Atoms

Article abstract of DOI:10.1021/jo00132a025

Vinyl ethers 3 can be synthesized in high yields by the cross-coupling of an aryl or benzyl halide with tris(2-ethoxyvinyl)borane (1) or (2-ethoxyvinyl)-1,3,2-benzodioxaborole (2) in the presence of 1 mol percent of a palladium complex such as PdCl2(PPh3)2, Pd(OAc)2(PPh3)2, or Pd(PPh3)4 and a base while retaining the original configuration of the double bond in (2-ethoxyvinyl)boranes.No noticeable quantities of biaryls or conjugated dienes were found in this reaction.The reaction did not proceed in the absence of a base.This new vinyl ether synthesis was found to be applicable to aryl halides substituted with a variety of functional groups such as halogen, methoxy, carboethoxy, and acetyl groups.Electron-attracting substituents facilitate the coupling.Since vinyl ethers 3 thus obtained can readily be hydrolyzed to give aldehydes (eq 4), the sequence (eq 1-4) provides an efficient new method for converting an aryl halide into an aldehyde with two more carbon atoms.