Palladium-Catalyzed Cross-Coupling Reactions of Aryl and Vinylic Boron Compounds with Organic Halides

Abstract

A general and convenient method for the stereo-and regioselective synthesis of conjugated alkadienes, alkenynes, arylated alkenes, and heterobiaryls is described. The reaction of (E) -or (Z) -1-alkenylboronates obtainable by hydroboration, with either (E) -or (Z) -1-alkenyl halides in the presence of a catalytic amount of tetrakis (triphenylphosphine) palladium and bases such as sodium alkoxides gives the corresponding (E, E) -, (E, Z) - (Z, E) -and (Z, Z) -alkadienes stereo-and regioselectively, while retaining the configuration of both the starting alkenylboronates and haloalkenes The similar reactions of (E) -and (Z) -1-alkenylboronates with 1-alkynyl, aryl, allylic, and benzylic halides also provide the corresponding couplig products stereosoelectively. The versatility of this method has been demonstrated by the synthesis of some natural products bearing conjugated alkadiene structures. The reaction of arylboronic acids with aryl halides to give unsymmetrical biaryls is also presented. A mechanism of this cross-coupling reaction, which involves the transmetallation between a 1-alkenylborane and an alkoxopalladium (II) complex generated through the metathetical displacement of a halogen atom of RPd (II) X with sodium alkoxide, is proposed.