Eiji Tayama

Activation of ether functionality of allyl vinyl ethers by chiral bis(organoaluminum) Lewis acids: application to asymmetric Claisen rearrangement

Chiral bis(organoaluminum) Lewis acids have been newly designed and synthetic utility of their eminent activation ability of an ether functionality has been successfully demonstrated by the application to asymmetric Claisen rearrangement of allyl vinyl ethers.

Bidentate organoaluminum Lewis acid for selective activation of carbonyl over acetal functionality: Chemoselective functionalization

Abstract Chemoselective functionalization of carbonyl compounds over acetals has been achieved by bidentate organoaluminum Lewis acid based on the selective double electrophilic activation of carbonyls.

New synthetic routes to optically active α-quaternary α-aryl amino acid derivatives via the diastereoselective Stevens and Sommelet–Hauser rearrangements

The Stevens rearrangement of N-allylic alpha-aryl amino acid-derived ammonium salts and the Sommelet-Hauser rearrangement of N-benzylic alpha-alkyl amino acid-derived ammonium salts are shown to proceed with remarkably high levels of diastereoselectivity. The methods presented in this work provide new routes to optically active alpha-quaternary alpha-aryl amino acid derivatives.

Selective Synthesis of [2]- and [3]Catenane Tuned by Ring Size and Concentration

The syntheses of [2]- and [3]catenanes by olefin metathesis and oxidative acetylide coupling have been studied in detail. Pseudorotaxanes that were obtained by mixing crown ether and ammonium salts containing two terminal reactive end-groups were converted to [2]- and [3]catenane. Their yields were influenced not only by the chain length of the ammonium salts but also by the concentration of the crown ether and the ammonium salts. The strain energies of [2]catenane were responsible for the formation of [2]catenane.

Metal-Free, One-Pot, Sequential Protocol for Transforming α,β-Epoxy Ketones to β-Hydroxy Ketones and α-Methylene Ketones

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to β-hydroxy ketones and α-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate (BF3·OEt2) generates the cationic intermediates by regioselective epoxide ring opening and an acyl shift. Then, a treatment of these cations with 2-aryl-1,3-dimethylbenzimidazolines (DMBIH) results in formation of 1,2-disubstituted 3-hydroxy ketones. DMBIH serves as a hydride donor in the second step of this process. Finally, the β-hydroxy ketones can be converted to 1,2-disubstituted 2-methylene ketones by treatment with methanesulfonic acid or a combination of methanesulfonyl chloride and triethylamine. Importantly, the sequential steps involved in formation of the α-methylene ketone products can be carried out in one pot.

Kinetic Resolution via the [2,3] Stevens Rearrangement of Epimeric Six-membered Ammonium Ylides: A New Entry to Enantio-enriched α-Amino Acid Derivatives

The asymmetric [2,3] Stevens rearrangement of epimeric mixtures of N-allylic ammonium salts derived from (5R)-5-phenyl-1,4-oxazin-2-one is shown to proceed with efficient kinetic resolution to afford the unnatural α-aminoacid derivatives in high enantio-purities.

Dramatic Enhancement of Reactivity of Organosilicon Compounds Induced by Complexation of Bis(allyl)silanes with Fluoride Ion

New type of fluoride ion catalyzed allylation agent (1a, 1b), allenylation agent (9, 10), and alkynylation agent (17) can be successfully utilized for various carbonyl substrates. The rate acceleration is ascribable to the shift of equilibrium to the chelate complexes with Bu4NF by the favorable chelation of bis(silyl) compounds toward the fluoride ion. The 19F NMR spectrum (ethyl trifluoroacetate as external standard) of a mixture of 1a and Bu4NF in CDCl3 showed two peaks at δ −81.75 and −77.67 (integration ratio∼9:1). The large signal corresponds to the original peak of Bu4NF and the small one might be ascribed to the chelate complex [B] between 1a and Bu4NF. The fluoride ion mediated reaction of bis(crotyldimethylsilyl)methane (7) with benzaldehyde was examined and the only γ-adduct 8 was obtained regioselectively.

Recent Advances in the Base-Induced Sommelet-Hauser Rearrangement of Amino Acid Derived Ammonium Ylides.

The Sommelet-Hauser rearrangement of N-benzylic ammonium ylides generated from ammonium salts is an interesting and useful transformation that enables one to convert a readily accessible C-N bond into a new C-C bond to an aromatic ring. The rearrangement was discovered by Sommelet in 1937, studied in detail by Hauser, and applied to organic synthesis by Sato until 1999. Further studies have not advanced because several competitive side reactions and structural limitations of the products severely limit the substrate scope and synthetic applications. In this Personal Account, a history of the research in problem solving and recent advances in the base-induced Sommelet-Hauser rearrangement are described. This synthetic method developed by my group provides efficient access to various types of α-aryl-α-amino acid and α-aryl-β-amino acid derivatives.

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

Summary Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives were investigated. The regioselectivities of these processes were found to be influenced by the structure of cyclopropanols as well as the counter anion of the copper(II) salts. A mechanism involving rearrangement reactions of radical intermediates and their competitive trapping by copper ions is proposed.

Remarkable template effect of a Lewis acid receptor in the intramolecular radical cyclization: control of reaction pathway as well as stereochemistry

Abstract A remarkable template effect in the intramolecular radical cyclization process has been observed by the successful utilization of Lewis acid receptor, aluminum tris(2,6-diphenylphenoxide) (ATPH). The origin of this efficient template effect by ATPH would be ascribable to the well-defined reaction environment created in front of the aluminum coordination center; this enables appropriate proximity of initially generated carbon radical to unsaturated carbon–carbon bond in the transition state for smooth cyclization and hence completely suppresses the undesired intermolecular reduction pathway. Moreover, such conformational restriction provided by the unique cavity of ATPH alters the stereoselectivity of the cyclization.