Momotaro Takeda

Rhodium-Catalyzed Asymmetric Arylation of N-Tosyl Ketimines

A rhodium-catalyzed addition of sodium tetraarylborates to N-tosyl ketimines is described. Highly efficient asymmetric catalysis has been achieved by employing a chiral diene ligand, constructing chiral amine derivatives possessing α-tetrasubstituted carbon stereocenters with high enantioselectivity.

Stereoselective synthesis of spirooxindoles by palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with isatins.

A new synthetic method of spirooxindole derivatives has been developed by way of a palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with isatins. By employing a newly prepared phosphoramidite ligand, the reaction proceeds smoothly with excellent diastereoselectivity. Preliminary results of its application to asymmetric catalysis using a chiral phosphoramidite ligand are also described.

Rhodium-Catalyzed Asymmetric Addition of Potassium Organotrifluoroborates to N-Sulfonyl Ketimines

A rhodium-catalyzed asymmetric addition of readily available potassium organotrifluoroborates to both N-tosyl and N-nosyl ketimines has been developed. High enantioselectivity has been achieved by using a chiral diene ligand, and the nosyl group of the addition products can be easily removed while retaining the enantiomeric purity.

Rhodium‐Catalyzed Asymmetric Synthesis of Spirocarbocycles: Arylboron Reagents as Surrogates of 1,2‐Dimetalloarenes

Enantiopure spirocycles that possess a quaternary spirocarbon stereocenter represent an important class of compounds as they can be found in various useful organic molecules, such as natural products, biologically active compounds, and effective chiral ligands for asymmetric catalysis. Construction of such spirocycles using transitionmetal-catalyzed asymmetric carbon–carbon bond-forming reactions are highly desirable in view of the efficiency of the process. In this context, sequential addition of 1,2-dimetalloarenes to 2-cycloalken-1-ones that are tethered at the 3-position to another electrophilic substituent, such as an alkyne, could rapidly afford spirocarbocycles in a convergent manner, as illustrated in Scheme 1; however, the preparation

Enantioselective Synthesis of α-Tri- and α-Tetrasubstituted Allylsilanes by Copper-Catalyzed Asymmetric Allylic Substitution of Allyl Phosphates with Silylboronates

A copper/N-heterocyclic carbene-catalyzed asymmetric allylic substitution of allyl phosphates with a silylboronate has been developed to give highly enantioenriched allylsilanes. High regioselectivity has been achieved by employing NaOH as the base, and this catalyst system is effective for both γ-mono- and disubstituted allyl phosphates.

Synthesis of quaternary carbon stereocenters by copper-catalyzed asymmetric allylic substitution of allyl phosphates with arylboronates.

A copper-catalyzed asymmetric allylic substitution of γ,γ-disubstituted allyl phosphates with arylboronates has been developed for the construction of quaternary stereocenters. High regio- and enantioselectivities have been achieved by employing a hydroxy-bearing chiral N-heterocyclic carbene ligand, and both E and Z substrates provide the same enantiomer as the major product. The mechanistic aspect of this catalysis has also been investigated to find that a 1:1 copper/ligand complex is most likely responsible for the present asymmetric catalysis, and the reaction proceeds with almost perfect 1,3-anti stereochemistry with respect to the allylic electrophile.

Silylative Cyclopropanation of Allyl Phosphates with Silylboronates

A potassium-bis(trimethylsilyl)amide-mediated cyclopropanation of allyl phosphates with silylboronates has been developed. Unlike the reported copper-catalyzed allylic substitution reactions, the nucleophile selectively attacks at the β-position of the allylic substrates under the present reaction conditions. The mechanism of this process has also been investigated, thus indicating the involvement of a silylpotassium species as the active nucleophilic component.

Synthesis of 3-mono-substituted binaphthyl-based secondary amine catalysts via monobromination of an axially chiral dicarboxylic acid derivative.

A facile synthetic route to a 3-bromo binaphthyl-based secondary amine through the monobromination of an axially chiral dicarboxylic acid derivative has been developed. The combination of this new procedure with coupling reactions established an efficient synthetic approach to a series of binaphthyl-based secondary amine catalysts containing various functional groups in an efficient way.