Seiji Shirakawa

Synthesis and resolution of a multifunctional inherently chiral calix[4]arene with an ABCD substitution pattern at the wide rim: the effect of a multifunctional structure in the organocatalyst on enantioselectivity in asymmetric reactions.

An efficient synthetic route to inherently chiral calix[4]arenes with an ABCD substitution pattern at the wide rim in the cone conformation was developed for the first time. For the synthesis of inherently chiral ABCD-type calix[4]arenes, first 5,11-dibromo-17-(3,5-dimethylphenyl)-25,26,27,28-tetrapropoxycalix[4]arene (9) was prepared as a key intermediate. Then, functionalization of the calix[4]arene 9 was examined, and highly regioselective monofunctionalization was achieved via selective monolithiation of bromo groups. Various multifunctionalized inherently chiral ABCD-type calix[4]arenes can be synthesized by using this method; thus, the synthesis of inherently chiral phosphine and carboxylic acid derivatives of ABCD-type calix[4]arene was demonstrated. In addition, the aminophenol derivative 1b of an ABCD-type calix[4]arene with a 3,5-dimethylphenyl group at the wide rim was synthesized and resolved into optically pure enantiomers. The chiral calix[4]arene 1b was used as an organocatalyst in asymmetric Michael addition reactions of thiophenols. The effect of the 3,5-dimethylphenyl group at the wide rim of calix[4]arene 1b on enantioselectivity was examined, and a positive effect of the 3,5-dimethylphenyl group was observed.

Water-soluble calixarenes as new inverse phase-transfer catalysts. Their application to aldol-type condensation and Michael addition reactions in water

Aldol-type condensation and Michael addition reactions of activated methyl and methylene compounds in aqueous NaOH solution have been developed without the need for any added organic solvents. The water-soluble calix[n]arenes, which contain trimethylammoniomethyl groups on the upper rim, were used as inverse phase-transfer catalysts, resulting in the corresponding products in good to excellent yields.

Improved design of inherently chiral calix[4]arenes as organocatalysts

Improvement of the design of inherently chiral calix[4]arenes as organocatalysts was accomplished via the introduction of a diarylmethanol structure. Novel, inherently chiral calix[4]arenes bearing a tertiary amine or a quaternary ammonium moiety, together with a diarylmethanol moiety, were synthesized from previously reported chiral calix[4]arene amino acid derivatives in an optically pure form. These chiral calix[4]arenes were applied to asymmetric reactions as organocatalysts, and a positive effect of the diarylmethanol structure on enantioselectivity was observed.

Rhodium-catalyzed biphasic hydroformylation of 4-octene using water-soluble calix[4]arene-phosphine ligands

The hydroformylation of water-insoluble internal olefins has n been realized in biphasic systems via n the use of rhodium complexes n of water-soluble calix[4]arene-phosphines. This catalytic system resulted in a good level of activity and reusability.

Water-Soluble Calixarenes as New Inverse Phase-Transfer Catalysts. Their Scope in Aqueous Biphasic Alkylations and Mechanistic Implications

Alkylation reactions of active methylene compounds, alcohols and phenols with alkyl halides in aqueous NaOH solution can be carried out without the need for any added organic solvents in most cases. The water-soluble calix[n]arenes, which contain trimethylammoniomethyl groups on the upper rim, were used as inverse phase-transfer catalysts, resulting in the corresponding alkylated products in good to high yields. The scope of this methodology in aqueous biphasic alkylation reactions and the mechanistic implications are discussed.

Hydrogen-bonding catalysis of sulfonium salts

Although quaternary ammonium and phosphonium salts are known as important catalysts in phase-transfer catalysis, the catalytic ability of tertiary sulfonium salts has not yet been well demonstrated. Herein, we demonstrate the catalytic ability of trialkylsulfonium salts as hydrogen-bonding catalysts on the basis of the characteristic properties of the acidic α hydrogen atoms on alkylsulfonium salts.

Synthesis and optical resolution of an inherently chiral calix[4]arene amino acid

The first synthesis and optical resolution of an inherently chiral calix[4]arene amino acid has been achieved.