2008 年 66 巻 2 号 p. 100-109
A novel Pd-catalyzed reaction of a 2-halo- or 2-trifloxy-l, 3-butadiene derivative with a soft nucleophile is developed. The reaction proceeds via an exo-alkylidene-π-allylpalladium intermedi-ate in a formal SN2' fashion to give an allenic compound exclusively. A variety of soft nucleophiles, such as malonates, phenoxides, and imides, are applicable to the reaction, and thus a wide range of functionality can be introduced to the products. The reaction is extended into an asymmetric counterpart and axially chiral allenes are prepared with up to 93% ee by the use of chiral palladium catalysts. A formal total synthesis of an insect pheromone is achieved using the Pd-catalyzed asymmetric reaction as a key step. The Pd-catalyzed reaction also enables to prepare axially chiral (allenylmethyl) silanes and allenylsilanes in optically active forms. Reactions of these silylallenes with appropriate electrophiles proceed via SE', pathways and the allenic axial chirality is efficiently transferred to stereogenic carbon centers in the SE', products.