Takeshi Katsuhira

Novel method for generation of secondary organozinc reagent : application to tandem carbon-carbon bond formation reaction of 1,1-dibromoalkane

Abstract Reaction of 1,1-dibromoalkane (R 1 CHBr 2 ) with trialkylzincate ((R 2 ) 3 ZnLi) followed by a palladium catalyzed coupling reaction of the resulting secondary organozinc reagent (R 1 CH(R 2 )ZnL) with various electrophiles (El-X) afforded R 1 CH(R 2 )El.

Generation and alkylation reaction of lithium 1-halocyclopropylzincate

Abstract Lithium dialkyl(1-halocyclopropyl)zincates which are generated from 1,1-dibromocyclopropanes undergo intramolecular alkylation to give 1-alkylcyclopropanes stereoselectively.

Stereochemistry in carbenoid formation by bromine/lithium and bromine/zinc exchange reactions of gem-dibromo compounds

Abstract Stereochemistry in generation of lithium and zincate carbenoids by bromine/metal exchange reactions of gem -dibromo compounds with BuLi and lithium triorganozincates, respectively, has been investigated. Both lithium and zincate carbenoids derived from 1,1-dibromoalkenes are demonstrated to be configurationally stable at low temperatures whereas, in the presence of the unreacted starting dibromoalkenes, the lithium carbenoids, but not the zincate carbenoids, undergo facile isomerization at the carbenoid carbons. Zincate carbenoids derived from 1,1-dibromocyclopropanes undergo isomerization slowly at the carbenoid carbons in the presence of the starting dibromocyclopropanes. The isomerization reactions of the lithium and zincate carbenoids are proved to proceed through a mechanism involving a bromine/metal exchange between the carbenoids and the starting dirbromo compounds. Highly stereoselective formation of the lithium carbenoids is observed in the reaction of 1,1-dibromoalkenes under the thermodynamic conditions. Under kinetically controlled conditions, both the bromine/lithium and bromine/zinc exchange reactions take place preferentially at the sterically more hindered bromine atom of the starting gem -dibromo compounds. The observation is rationalized by an exchange mechanism involving a linear transition state of either an ate complex formation or an S N 2 reaction at the more hindered bromine atom where strain relief due to the elongation of the carbon-bromine bond is expected.

Stereoselective synthesis of gem-disubstituted cyclopropanes from gem-dibromocyclopropanes

Abstract The title reaction is realized by utilizing an intramolecular alkylation reaction of zincate carbenoids followed by a Pd(0)-catalyzed coupling reaction with acyl, aryl, and alkenyl halides.