Koji Hirano

Nickel-Catalyzed Carboxylation of Organozinc Reagents with CO2

An efficient nickel catalyst system for the carboxylation of organozinc reagents with CO(2) under very mild conditions has been developed. The catalyst system complements the conventional methods and enables the direct synthesis of various saturated carboxylic acid derivatives from the corresponding alkylzinc reagents and CO(2).

Synthesis of arylallenes by palladium-catalyzed retro-propargylation of homopropargyl alcohols.

Treatment of tertiary homopropargyl alcohol with aryl halide under palladium catalysis provided arylallenes regioselectively. The reaction includes retro-propargylation, which proceeds in a concerted fashion via a cyclic transition state and transfers the stereochemistry of homopropargyl alcohols through C-C bond cleavage. The present method enables the use of homopropargyl alcohols as allenylmetal equivalents.

Nickel-Catalyzed Allylation of Allyl Carbonates with Homoallyl Alcohols via Retro-Allylation Providing 1,5-Hexadienes

A highly efficient and mild method for the synthesis of 1,5-hexadienes, nickel-catalyzed reactions of Boc-protected allyl alcohols with homoallyl alcohols, has been developed. Nickel-mediated retro-allylation allows for the use of homoallyl alcohols as allylmetal equivalents in the synthesis of 1,5-hexadienes.

Palladium-catalyzed formal cycloaddition of silacyclobutanes with enones: synthesis of eight-membered cyclic silyl enolates.

Treatment of silacyclobutanes with enones under palladium catalysis resulted in formal cycloaddition to yield the corresponding eight-membered ring. The reaction provides a facile and convergent access to synthetically useful eight-membered cyclic silyl enolates.

Nickel-catalysed reactions with trialkylboranes and silacyclobutanes.

Nickel catalysis enables us to develop new reactions with trialkylboranes and silacyclobutanes of modest reactivity. A combination of Ni(cod)(2) and tri-tert-butylphosphine catalyses alkylation reactions of aldehydes and alpha,beta-unsaturated esters with various trialkylboranes of modest reactivity, suppressing conceivable beta-hydride elimination from alkylnickel intermediates. A nickel catalyst is also useful for 1,4-addition of bis(pinacolato)diboron to alpha,beta-unsaturated esters and amides. Nickel-catalysed reaction of silacyclobutanes with aldehydes results in ring opening to afford the corresponding alkoxyallylsilanes. In contrast, the ring expansion reaction of benzosilacyclobutene with aldehydes yields benzoxasilacyclohexenes. A nickel catalyst prepared from Ni(cod)(2) and tricyclohexylphosphine realises direct silylation of terminal alkenes with silacyclobutane furnishing vinylsilanes.

Nickel-catalyzed cross-coupling reaction of aryl halides with allylic zirconium reagents generated in situ from zirconocene(alkene) complexes

Allylic zirconium reagents that are generated in situ via allylic C-H bond activation of alkenes proved to serve as metal counterparts in nickel-catalyzed cross-coupling reactions.