Shohei Sase

Catalyst-free syntheses of [2]rotaxanes utilizing a pentacoordinated hydrosilane as an end-capping agent.

A pentacoordinated hydrosilane activated by an intramolecular nitrogen-silicon dative bond was utilized as an end-capping agent for catalyst-free syntheses of [2]rotaxanes. The end-capping reaction of a pseudo[2]rotaxane bearing a salicylic acid terminus with the pentacoordinated hydrosilane readily proceeded at room temperature to produce the corresponding silyl-capped [2]rotaxane.

Synthesis of a Stable Selenoaldehyde by Self‐Catalyzed Thermal Dehydration of a Primary‐Alkyl‐Substituted Selenenic Acid

The unprecedented dehydration of a selenenic acid (RCH2SeOH) to a selenoaldehyde (RCH=Se) has been demonstrated. A primary-alkyl-substituted selenenic acid was synthesized for the first time by taking advantage of a bulky cavity-shaped substituent. Upon heating in solution, the selenenic acid underwent thermal dehydration to produce a stable selenoaldehyde, which was isolated as stable crystals and crystallographically characterized. Investigation of the reaction mechanism revealed that this β dehydration reaction involves two processes, both of which reflect the characteristics of a selenenic acid: 1) dehydrative condensation of two molecules of selenenic acid to generate a selenoseleninate intermediate [RCH2SeSe(O)CH2R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a C=Se double bond, which establishes the self-catalyzed β dehydration of the selenenic acid.

Efficient End‐Capping Synthesis of Neutral Donor–Acceptor [2]Rotaxanes Under Additive‐Free and Mild Conditions

Efficient end-capping synthesis of neutral donor-acceptor (D-A) [2]rotaxanes without loading any catalysts or activating agents was achieved by utilizing high reactivity of a pentacoordinated hydrosilane toward salicylic acid derivatives. As components of [2]rotaxanes, an electron-deficient naphthalenediimide-containing axle with a salicylic acid terminus and several electron-rich bis(naphthocrown) ether macrocycles were employed. End-capping reactions with the pentacoordinated hydrosilane underwent smoothly even at low temperature to afford the corresponding [2]rotaxanes in good yields. A [2]rotaxane containing bis-1,5-(dinaphtho)-38-crown-10 ether as a wheel molecule was synthesized and isolated in 84% yield by the end-capping at -10 °C, presenting the highest yield ever reported for the end-capping synthesis of a neutral D-A [2]rotaxane. It was found that the yields of the [2]rotaxanes in the end-capping reactions were almost parallel to the formation ratios of the corresponding pseudo[2]rotaxanes estimated by utilizing model systems. These results indicate that the end-capping reaction using the pentacoordinated hydrosilane proceeded without perturbing the threading process, and most of the pseudo[2]rotaxanes underwent efficient end-capping reaction even at low temperature.

Synthesis of a Stable Primary-Alkyl-Substituted Selenenyl Iodide and Its Hydrolytic Conversion to the Corresponding Selenenic Acid.

A primary-alkyl-substituted selenenyl iodide was successfully synthesized through oxidative iodination of a selenol with N-iodosuccinimide by taking advantage of a cavity-shaped steric protection group. The selenenyl iodide exhibited high thermal stability and remained unchanged upon heating at 100 °C for 3 h in [D8]toluene. The selenenyl iodide was reduced to the corresponding selenol by treatment with dithiothreitol. Hydrolysis of the selenenyl iodide under alkaline conditions afforded the corresponding selenenic acid almost quantitatively, corroborating the chemical validity of the recent proposal that hydrolysis of a selenenyl iodide to a selenenic acid is potentially involved in the catalytic mechanism of an iodothyronine deiodinase.

Synthesis and Properties of Pentacoordinated Phenoxysilane and Carboxysilanes with Intramolecular Nitrogen–Silicon Coordination

Reactions of a neutral pentacoordinated monohydrosilane bearing a dative N‒Si bond with phenol and benzoic acid derivatives gave the corresponding pentacoordinated phenoxysilane and carboxysilanes, respectively. X-ray crystallographic analyses of these silanes revealed that the distance of the N‒Si dative bond is shortened and the pentacoordination character of the silicon center becomes greater with the increase in the electron-withdrawing character of the apical substituent on silicon.

Transnitrosation from a stable thionitrate to an amine with concomitant formation of a sulfenic acid

The reaction of a stable thionitrate bearing a bowl-shaped steric protection group with dibutylamine resulted in nitrosation of the amine with concomitant formation of a sulfenic acid, presenting the experimental evidence for the proposed mechanism of the reaction of thionitrates with amines. GRAPHICAL ABSTRACT

Modeling of the Bioactivation of an Organic Nitrate by a Thiol to Form a Thionitrate Intermediate

Thionitrates (R–SNO2) have been proposed as key intermediates in the biotransformation of organic nitrates that have been used for the clinical treatment of angina pectoris for over 100 years. It has been proposed and widely accepted that a thiol would react with an organic nitrate to afford a thionitrate intermediate. However, there has been no example of an experimental demonstration of this elementary chemical process in organic systems. Herein, we report that aryl- and primary-alkyl-substituted thionitrates were successfully synthesized by the reaction of the corresponding lithium thiolates with organic nitrates by taking advantage of cavity-shaped substituents. The structure of a primary-alkyl-substituted thionitrate was unambiguously established by X-ray crystallographic analysis.

Crystal structure of {3-[3,5-bis­(2,6-di­methyl­phen­yl)-1,2-phenyl­ene]-1-(2,6,2′′,6′′-tetra­methyl-1,1′:3′,1′′-ter­phen­yl-5′-yl)imidazol-2-yl­idene}chlorido­(η6-p-cymene)ruthenium(II) benzene disolvate

The title compound, [Ru(C47H43N2)Cl(C10H14)]·2C6H6, crystallized with two independent molecules of benzene. One of the N-aryl moieties of the N-heterocyclic carbene (NHC) ligand underwent cyclometallation to form a five-membered ruthenacycle. The complex has a three-legged piano-stool structure with two C atoms incorporated in the five-membered ruthenacycle and a Cl atom as legs. The ruthenacycle is essentially coplanar with the imidazole ring of the NHC ligand, making a dihedral angle of 0.85 (8)°.

Syntheses of Biologically Relevant Reactive Sulfur Species by Utilizing a Primary Alkyl Steric Protection Group

Abstract A novel primary alkyl steric protection group (BpqCH2 group) bearing a cavity-shaped framework was designed and successfully applied to the stabilization of a sulfenyl iodide. The sulfenyl iodide showed remarkable stability, demonstrating that the BpqCH2 group is very effective for kinetic stabilization of primary-alkyl-substituted reactive species.