Shotaro Hirao

An anomalous hydration/dehydration sequence for the mild generation of a nitrile oxide

A nitrile oxide containing a carbamoyl group is readily generated upon the treatment of 2-methyl-4-nitro-3-isoxazolin-5(2H)-one with water under mild reaction conditions, even in the absence of special reagents. The obtained nitrile oxide undergoes cycloaddition with dipolarophiles, alkynes and alkenes, to afford the corresponding isoxazol(in)es, which are useful intermediates in the synthesis of polyfunctionalized compounds. A plausible mechanism underlying the formation of the nitrile oxide is proposed, which involves an anomalous hydration/dehydration sequence. DFT calculations were also performed to support this mechanism.

Development of a new palladium catalyst supported on phenolic resin

A phenolic resin-supported palladium catalyst, in which hydroxyl groups contribute to the stabilization of palladium nanoparticles, was developed. The catalyst could be used repeatedly, and thus has a large turn over number (TON). When a composite of polyethylene terephthalate and phenolic resin was employed as a support, the catalyst was easily deformed on demand.

Enantiopure O-Ethyl Phenylphosphonothioic Acid: A Solvating Agent for the Determination of Enantiomeric Excesses

An improved method, which is highly reproducible, was developed for the enantioseparation of racemic O-ethyl phenylphosphonothioic acid (1a) with brucine by introducing seeding to a supersaturated solution of the diastereomeric salt mixture. The present method gave both diastereomeric salts in high yields with a diastereomeric ratio of >99.5:0.5 upon choosing the crystallization solvent (MeOH for the (R)-1a salt and MeOH/H2 O for the (S)-1a salt). The enantiopure acid showed a good chirality recognition ability for not only strong bases, such as amines and amino alcohols, but also weakly basic alcohols and was applicable as a solvating agent to the (1) H NMR determination of the enantiomeric excess of chiral amines, amino alcohols, and alcohols, including aliphatic substrates.

An NMR study on a pseudo-intramolecular transacylation reaction of an α-aryl-β-keto ester

The pseudo-intramolecular transacylation reaction efficiently proceeds like an intramolecular reaction, even though it is actually an intermolecular reaction. We have obtained valuable insights by monitoring the reaction by 1H NMR spectroscopy.