Yuuki Takayama

Stereoselective synthesis of optically active substituted piperidines and pyrrolidines from amino acid derivatives by titanium(II)-mediated intramolecular cyclization reaction

Abstract A versatile and high-yielding synthesis of optically active substituted piperidines and pyrrolidines from amino acid derivatives employing titanium(II)-mediated intramolecular cyclization of bis-unsaturated carbonates was developed.

Effect of Molecule–Electrode Contacts on Single-Molecule Conductivity of π-Conjugated System Measured by Scanning Tunneling Microscopy under Ultrahigh Vacuum

A π-conjugated compound with two thioacetate end groups was synthesized using a recently developed method. A self-assembled monolayer (SAM) of corresponding dithiol was prepared by dipping a Au(111) surface for 1 min in a 2 mM dithiol toluene solution formed 30 min after the addition of a drop of 30% NH4OH in water to the dithioacetate toluene solution. We investigated electronic conduction through isolated single molecules of the π-conjugated compound by statistical analysis of molecular junctions repeatedly formed between a gold tip and the SAM on Au(111) using scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV). The single-molecular conductivity of the π-conjugated compound is described as Gm=Tcontact with tipTπ-systemTcontact with substrateG0 according to the Landauer equation. Here, Ts are transmission functions and G0 is the quantum conductance, i.e., 2e2/h. Because of observed high values of Gm for the π-conjugated compound, we could readily analyze the effect of molecule–electrode contacts on Tcontact with tipTcontact with substrate. Namely, we successfully observed the dependence of Tcontact with tipTcontact with substrate on binding sites of –S- on a Au(111) surface, i.e., the bridge (or the hollow) and the top sites.

An efficient synthesis of optically active five- and six-membered cyclic compounds with selectable stereo-controls by a Ti(II)-mediated cyclization of chiral secondary 2,7- and 2,8-enyn-1-ol derivatives

Abstract Ti(II)-mediated cyclization of readily accessible optically active secondary 2,7- and 2,8-enyn-1-ol derivatives enables the selective preparation of any one of the four possible stereoisomers of the cyclized product with high optical purity.

Electronic Conduction through Single Molecule of New π-Conjugated System Measured by Scanning Tunneling Microscopy

In recent years, π-conjugated organic compounds have become a widely investigated class of advanced materials as they exhibit a variety of interesting electronic properties. One of the most attractive properties is their small highest occupied molecular orbital-lowest unoccupied molecular orbital gap, which results in the very high charge transport efficiency of the π-conjugated compounds as compared with that of saturated compounds. A new π-conjugated compound was synthesized by a recently developed method. We investigated electronic conduction through an isolated single molecule of the π-conjugated compound by scanning tunneling microscopy (STM) and self-assembly techniques.

Asymmetric synthesis of stereodefined α-alkyl-γ-benzyloxymethyl-β-trimethylsilyl-γ-butyrolactones that serve as an efficient precursor for constructing carbon skeletons having a tertiary or quaternary stereogenic center

The optically active lactone 1 can be transformed to a chiral building block or intermediate for constructing carbon skeletons containing either a tertiary or quaternary stereogenic center by taking advantage of the steric bulk as well as the reactivity of a trimethylsilyl group at the β-position of 1.