Development of Transition-Metal-Catalyzed Reactions of Preparing Allenes and Their Derivatives

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Previously, we reported a palladium-catalyzed reaction of 2-bromo-1,3-dienes, which could be easily derived from a variety of aldehydes, with soft nucleophiles giving functionalized allenes. The reaction was extended to an asymmetric counterpart by using a chiral palladium catalyst and the corresponding axially chiral allenes were obtained with excellent enantioselectivity.It was found analogous bromodiene substrates could be prepared from allylsilanes. It was demonstrated that 1,3-dien-2-y1 triflates, which were easily obtained in high yields from vinylketones, showed analogous reactivity to the bromodienes in the Pd-catalyzed reaction. These provided a route to multi-substituted allenes, which were inaccessible by the route from aldehydes.The Pd-catalyzed allene synthesis reaction was applied to asymmetric total synthesis of the sex pheromone of male dried bean beetle.For the Pd-catalyzed asymmetric synthesis of the axially chiral allenes, biaryl bisphosphines, such as binap, were effective for high enantioselectivity. It was found that introduction of bulky substituents at the 3-and 3'-positions of the biaryl skeleton improved the performance of the biaryl chiral phosphines in the Pd-catalyzed reaction.An intermediate of the Pd-catalyzed reaction, alkylidene-π-allylpalladium species, was isolated and its solution dynamics was studied. Based on the results, a novel reaction of 2-bromo-1,3,5-trienes with soft nucleophiles giving conjugated vinylallenes was developed. The reaction was successfully extended to the asymmetric reaction.It was known that 1,4-hydrosilylation of conjugated enynes afforded allenylsilanes. Newly developed chiral phosphaferrocenes were applied to the asymmetric hydrosilylation of enynes and axially chiral allenylsilanes were obtained with excellent enantioselectivity.Treatment of appropriate zirconacyclopentane species with propargyl electrophiles in the presence of copper(I) salts gave bis-allene products in a stereospecific fashion.