Kenji Mishiro

Total Synthesis of Ellagitannins through Regioselective Sequential Functionalization of Unprotected Glucose

Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose. The key reactions are β-selective glycosidation of a gallic acid derivative by using unprotected glucose as a glycosyl donor and catalyst-controlled regioselective introduction of a galloyl group into the inherently less reactive hydroxy group of the glucoside.

Asymmetric desymmetrization of meso-diols by C(2)-symmetric chiral 4-pyrrolidinopyridines.

Summary In this work we developed C 2-symmetric chiral nucleophilic catalysts which possess a pyrrolidinopyridine framework as a catalytic site. Some of these organocatalysts effectively promoted asymmetric desymmetrization of meso-diols via enantioselective acylation.

A Cyclochiral Conformational Motif Constructed Using a Robust Hydrogen-Bonding Network

A novel conformational motif constructed with a robust intramolecular hydrogen-bonding (H-bonding) network was discovered. A pyrrolidine derivative possessing four identical amide substituents at C(2) and C(5) formed a strong intramolecular H-bonding network consisting of all the amide groups. This conformation yielded a cyclochiral structure with a handedness that depended on the directionality of the H-bonding network. The most stable compound was isolated and applied to the acylative kinetic resolution of secondary alcohol. The handedness of the H-bonding network was biased by the presence of chiral substituents, and the preferred direction could be switched under an external stimulus. A structural analysis using NMR, X-ray crystallography, and theoretical calculation techniques indicated that the conformation of the substituents was highly ordered and depended on the directionality of the H-bonding network.

Phototriggered Ketone Formation from an Aminocyclopropenone and a Carboxylic Acid

A novel phototriggered functionalization reaction of a carboxylic acid using an aminocyclopropenone has been developed. Irradiation of an aminocyclopropenone and carboxylic acid mixture generated ketones that possessed substituents from both the carboxylic acid and the aminocyclopropenone. This reaction occurred through two distinct phototriggered processes. Using this reaction, substituents in an aminocyclopropenone can be connected with a carboxylic acid containing molecule.

Phototriggered Dehydration Condensation Using an Aminocyclopropenone

A phototriggered dehydration condensation using an aminocyclopropenone has been developed. The UV irradiation of an aminocyclopropenone generated a highly reactive ynamine in situ and the dehydration condensation of a carboxylic acid and an amine coexisting in the reaction solution smoothly proceeded to afford an amide. This reaction is completely controllable by the ON/OFF states of a UV lamp.

A Concise Access to C2-Symmetric Chiral 4-Pyrrolidinopyridine Catalysts with Dual Functional Side Chains

A practical method was developed for the preparation of a diastereomeric library of C2-symmetric chiral 4-pyrrolidinopyridine catalysts with dual amide side chains. Use of a racemic precursor is the key to the concise production of catalysts with diverse stereochemisty.