Kenji Seki

Bio: Kenji Seki is an academic researcher from Osaka University. The author has contributed to research in topics: Adduct & Spiro compound. The author has an hindex of 2, co-authored 4 publications receiving 43 citations. Previous affiliations of Kenji Seki include Kansai University.

Stereocontrolled oxazolidinone formation by the addition of 4,5-disubstituted iminodioxolane to oxirane via a spiro compound

Abstract: 4,5-Disubstituted 2-imino-1,3-dioxolanes readily add to oxiranes in the presence of AlCl 3 , furnishing 1,3-oxazolidin-2-ones in a stereospecific manner, where the configurations of oxiranes and iminodioxolanes are responsible for the configuration of products and the feasibility of the addition, respectively. A preliminary adduct, a spiro compound intermediate, is isolated, and its decompostion to oxazolidinone is demonstrated

Stereospecific Cycloaddition of Heterocumulenes to Oxiranes Catalyzed by Organotin Halide Complexes.

Abstract: Stereospecific cycloaddition of 2,3-disubstituted oxiranes to heterocumulenes, including carbodiimides, isocyanates and carbon dioxide, is catalytically promoted by dialkyltin diiodide-hexamethylphosphoric triamide (HMPA) system, producing various five-membered heterocycles, where the configuration of the carbons in the oxirane ring is retained. In particular, the addition of isocyanates to oxiranes gave stereo-specifically two types of products, dioxolan-2-imines and oxazolidin-2-ones independently, while the rearrangement of the former to the latter product has been already proposed.

Stereocontrolled Oxazolidinone Formation by the Addition of 4,5‐Disubstituted Iminodioxolane to Oxirane via a Spiro Compound.

Abstract: 4,5-Disubstituted 2-imino-1,3-dioxolanes readily add to oxiranes in the presence of AlCl 3 , furnishing 1,3-oxazolidin-2-ones in a stereospecific manner, where the configurations of oxiranes and iminodioxolanes are responsible for the configuration of products and the feasibility of the addition, respectively. A preliminary adduct, a spiro compound intermediate, is isolated, and its decompostion to oxazolidinone is demonstrated

Influence of temperature and pressure on cyclic carbonate synthesis catalyzed by bimetallic aluminum complexes and application to overall syn-bis-hydroxylation of alkenes.

Abstract: The effect of moderate temperatures (22–100 °C) and pressures (1–10 bar) on the synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by a combination of bimetallic aluminum complexes and tetrabutylammonium bromide is investigated. The combined bimetallic complex and tetrabutylammonium bromide catalyst system is shown to be an order of magnitude more active than the use of tetrabutylammonium bromide alone at all temperatures and pressures studied. At the higher temperatures and pressures used, disubstituted epoxides become substrates for the reaction and it is shown that reactions proceed with retention of the epoxide stereochemistry. This allowed a route for the overall syn-bis-hydroxylation of alkenes to be developed without the use of hazardous metal based reagents. At higher pressures it is also possible to use compressed air as the carbon dioxide source.

Palladium(0)-Catalyzed Asymmetric Cycloaddition of Vinyloxiranes with Heterocumulenes Using Chiral Phosphine Ligands: An Effective Route to Highly Enantioselective Vinyloxazolidine Derivatives

Abstract: Cycloaddition reaction of 2-vinyloxiranes with carbodiimides using Pd2(dba)3·CHCl3, and TolBINAP as the chiral ligand, in THF at ambient temperature, afforded 4-vinyl-1,3-oxazolidin-2-imines in 70−99% yield and in up to 95% ee. The stereoselectivity is strongly influenced by the structure of the chiral phosphine ligands and substrates, as well as by the reaction conditions. The enantiodetermination step is assumed to be nucleophilic attack of a nitrogen nucleophile on a π-allyl palladium intermediate. Reaction of 2-vinyloxiranes with isocyanates using the same catalyst system afforded 4-vinyl-1,3-oxazolidin-2-ones in high yield but in no greater than 50% ee.

Stereochemical Divergence in the Formation of Organic Carbonates Derived from Internal Epoxides

Abstract: Catalysis of the challenging cycloaddition of carbon dioxide to internal epoxides has been studied using iron(III) amine triphenolate complexes and particular focus has been given to the stereochemical regulation of this process When pure cis- or trans-2,3-epoxybutane is used as substrate, the stereochemistry of the product can be controlled yielding selectively cis- or trans-cyclic carbonates for both epoxidic substrates This stereochemical divergence relates to two accessible catalytic pathways leading to either the cis or trans product via two distinct ring-closure steps The involved mechanism and stereocontrol is a function of the catalyst/co-catalyst loading, and is further influenced by the medium, temperature and catalyst/co-catalyst structure Other trans-internal epoxides could also be successfully converted into the pure trans-cyclic carbonate products without any loss of stereochemical information

Tributylphosphine-Catalyzed Cycloaddition of Aziridines with Carbon Disulfide and Isothiocyanate

Abstract: Aziridines underwent cyclization reaction with carbon disulfide and isothiocyanate in the presence of organophosphine to afford thiazolidinone derivatives in good to high yields. The mechanistic study revealed that organophosphine serves as a catalyst in the reaction.

Bimetallic Aluminum(salen) Catalyzed Synthesis of Oxazolidinones from Epoxides and Isocyanates

Abstract: The bimetallic aluminum(salen) complex [Al(salen)]2O is shown to catalyze the synthesis of oxazolidinones from epoxides and isocyanates. The reaction is demonstrated to proceed with overall retention of epoxide stereochemistry, and both aromatic and aliphatic isocyanates can be used as substrates. In contrast to the corresponding reactions between epoxides and carbon dioxide or carbon disulfide which are also catalyzed by [Al(salen)]2O, no cocatalyst is needed in the reactions with isocyanates. A mechanism is proposed which involves breaking and reforming of the Al–O–Al unit during the catalytic cycle, and this is supported by results obtained using monometallic catalysts.