Construction of Polycycles Using Palladium-Catalyzed α-Arylation Reaction toward Carbonyl Group

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In the last decade, organometallic chemistry, especially organopalladium chemistry has made a marked advance. While a great number of palladium-catalyzed arylation and vinylation reactions have been investigated, most of which involve olefins (Heck reaction), organo-tin compounds (Stille reaction), or organo-borane compounds (Suzuki reaction) as terminators.Exploitation of other functional groups as the terminator is expected to enable expanded application. Recently, the intermolecular palladium-catalyzed α-arylation reaction of ketone was reported by three groups of US and Japan. At the same time, we also reported independently its intramolecular version to form benzene-annulated bridged- spirocycloalkanones employing a bis(triphenylphosphine)palladium(II) chloride-cesium carbonate-with or without triphenylphosphine catalyst system.Our catalyst system was found to be applicable to properly designed substrates bearing a formyl or nitro terminating group. Arylation toward the formyl group occurred at the α-position (α-arylation) or at the carbonyl carbon (carbonyl-arylation) depending on the structure of the substrates and on the reaction solvent. The α-arylated secondary nitro group was partially transformed to ketone, whereas the tertiary nitro group was partially eliminated to a styrene type of olefin.Now, we can get various types of carbocycles employing the above intramolecular arylation conditions. They bear the useful functional groups, ketone, formyl, and nitro groups. We are now engaged in the synthetic investigation of Hetisan type of aconite alkaloids using the above cyclization reaction.