Hajime Iwamoto

Niigata University · Department of Chemistry

We have developed protocols for promoting redox reactions utilizing the 2-substituted 1,3-dimethylbenzimidazoline (BIH–R) and benzimidazolium (BI+–R) couples which were applied to the desulfonylative radical Truce-Smiles rearrangement. Expected rearrangement products formed in modest to good yields in these processes, in which added or in situ gene...

Photocatalytic systems consisting of 2-substituted benzimidazoliums (BI⁺–R, R = polycyclic aryl, triarylamine or phenyl-sulfate) and stoichiometric hydride donor reagents were developed. Light emitting diode irradiation of these photocatalysts in the presence of NaBH4 or picoline borane promotes desulfonylation reactions of an N-sulfonyl indole, N-...

Triarylamine-substituted benzimidazoliums (BI+-PhNAr2), new electron donor-acceptor dyad molecules, were synthesized. Their photocatalytic properties for reductive organic transformations were explored using absorption and fluorescence spectroscopy, redox potential determinations, density functional theory calculations, transient absorption spectro...

A new photocatalytic system was developed for carrying out desulfonylative α-oxyamination reactions of α-sulfonylketones in which α-ketoalkyl radicals are generated. The catalytic system is composed of benzimidazolium aryloxide betaines (BI+-ArO-), serving as visible light-absorbing electron donor photocatalysts, and 2,2,6,6-tetramethylpiperidine 1...

Desulfonylation reactions of α-sulfonylketones promoted by photoinduced electron transfer with 2-hydroxyarylbenzimidazolines (BIH-ArOH) were investigated. Under aerobic conditions, photoexcited 2-hydroxynaphthylbenzimidazoline (BIH-NapOH) promotes competitive reduction (forming alkylketones) and oxidation (producing α-hydroxyketones) of sulfonylket...

N -Sulfonylated [3]catenanes, which exist as two translational isomers, were synthesized. The X-ray crystal structure of the distal isomer of [3]catenane, which has higher symmetry, revealed hydrogen bonds involving the carboxylic...

A debrominative oxygenation protocol has been developed for the conversion of α-bromo-α,α-dialkyl-substituted carbonyl compounds to their corresponding α-hydroxy analogues. For example, stirring a solution of α-bromoisobutyrophenone and 2-aryl-1,3-dimethylbenzimidazoline (BIH-Ar) at room temperature under an air atmosphere leads to the efficient fo...

An unprecedented photocatalytic system consisting of benzimidazolium aryloxide betaines (BI+–ArO–) and stoichiometric hydride reducing reagents was developed for carrying out desulfonylation reactions of N-sulfonyl-indoles, -amides and -amines, and -sulfonylketones. Measurements of absorption spectra and cyclic voltammograms as well as DFT calcula...

A visible light promoted process for desulfonylation of N-sulfonylamides and -amines has been developed, in which 1,3-dimethyl-2-hydroxynaphthylbenzimidazoline (HONap-BIH) serves as a light absorbing, electron and hydrogen atom donor, and a household white light-emitting diode serves as a light source. The process transforms various N-sulfonylamide...

Benzimidazolium naphthoxide (–ONap-BI+) was first synthesized and utilized as an unprecedented betaine photo-redox catalyst. Photoexcited state of –ONap-BI+ generated by visible light irradiation catalyzes the reductive deiodination as well as desulfonylation reactions in which 1,3-dimethyl-2-phenylbenzimidazoline (Ph-BIH) cooperates with as an ele...

No abstract is available for this article.

Visible light promoted reduction reactions of organohalides, sulfonamides, organonitriles and epoxy ketones were performed using 1,3-dimethylbenzimidazolines possessing 2-hydroxynaphthyl or 2-hydroxyphenyl substituents (HOAr-DMBIH) as photo-reductants. Xe or Hg–Xe lamp through an appropriate glass-filter (λ>390 nm) and a household white light-emitt...

Oxidative ring-opening reactions of benzene-fused bicyclic cyclopropyl silyl ethers, promoted by copper(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bon...

[5]Catenanes were synthesized by olefin metathesis dimerization. The reaction of pseudorotaxanes, which were derived from a [2]catenane and one equivalent of an ammonium salt bearing two terminal olefins in dichloromethane, with a catalytic amount of Grubbs catalyst afforded linear [5]catenanes in 12% yield. Intermolecular and intramolecular olefin...

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to β-hydroxy ketones and α-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate (BF3•OEt2) generates the cationic intermediates by regioselective epoxide ring opening and acyl shift. Then, a treatment of these cations w...

The visible light-promoted reduction reactions of some organohalides were investigated using 2-aryl-1,3-dimethylbenzimidazolines (Ar-DMBIH) possessing 2-naphthyl or 2-hydroxynaphthyl substituents. In these reduction reactions, single-electron transfer from photo-excited Ar-DMBIH, attained by Xe lamp irradiation through an appropriate glass-filter (...

A facile protocol for the synthesis of substituted cyclopropanes via reaction of electron rich alkenes with α-aryl diazoesters is presented.

A combination of 2-aryl substituted 1,3-dimethyl-benzimidazolines (DMBIHs) and tris(2,2'-bipyridine) ruthenium(II) chloride, Ru(bpy)(3)Cl-2 was used to promote photoinduced electron-transfer (PET) reactions of alpha-halomethyl-substituted benzocyclic 1-alkanones. This photo-reagent system stimulates free radical forming, cleavage of both carbon-bro...

The base-induced asymmetric [2,3] Stevens rearrangement of N-cinnamyl tetraalkylammonium ylides derived from l-alanine amides proceeds via a double axially chiral intermediate to afford the corresponding α-substituted alanine derivatives with high enantio- and diastereoselectivities.

A photoreaction between benzoyl compounds, such as benzoylformate derivatives, and 2-(p-anisyl)-1,3-dimethylbenzimidazoline in the presence of allyl bromide was found to give various allylated alcohols. In the reaction of benzoylformates, cc-hydroxy ester enolates, for which the negative charge occurs on the carbonyl carbon of benzoyl (umpolung rea...

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives were investigated. The regioselectivities of these processes were found to be influenced by the structure of cyclopropanols as well as the counter anion of the copper(II) salts. A mechanism involving rearrangement reactions of radical intermediates and t...

Title compounds such as (V) and (IX) are prepared via a new three-step sequence including base-induced Sommelet—Hauser rearrangement, subsequent von Braun reaction and intramolecular α-alkylation.

The syntheses of [2]- and [3]catenanes by olefin metathesis and oxidative acetylide coupling have been studied in detail. Pseudorotaxanes that were obtained by mixing crown ether and ammonium salts containing two terminal reactive end-groups were converted to [2]- and [3]catenane. Their yields were influenced not only by the chain length of the amm...

The 1,4-elimination reaction of (Z)-N-Boc-2-(4-methoxy-2-alkenyloxy)amines with Brønsted acids catalyzed aza-Ferrier reaction of the 1,4-eliminated product, thus obtained, afforded various β-amino-β,γ-unsaturated aldehydes. The scope and limitation of this sequential reaction are described.

Various N-functionalized anilines such as (Ib)—(Ie) and (IV) or electron-rich alkoxybenzenes (VI) undergo a Cu(II)-catalyzed electrophilic aromatic substitution with diazoesters in the presence of acidic catalysts under optimized conditions.

Aza-Prins cyclization reactions of N-tosyl-3-butenylamine with p-methoxybenzaldehyde, 1-naphthaldehyde and 2-naphthaldehyde take place efficiently using a combination 1-butyl-3-methylimidazolium of ferric chloride and hexafluorophosphate in benzotrifluoride (Felm-BTF procedure). The new methodology, leading to formation of target N-tosyl-4-chloro-2...

The intermolecular aromatic substitution of N,N-dialkylanilines and alkoxybenzenes with diazoesters is shown to proceed in the presence of catalytic amounts of both copper(II) salt and acid (Lewis or Brønsted). This method is a mild and rare metal-free C–C bond formation reaction between aromatic (sp2) and aliphatic (sp3) carbons.

Selective amine de-alkylation enables the conversion of Sommelet–Hauser rearrangement products into 2-aryl-2-bromoacetic acid derivatives. These compounds are valuable synthetic intermediates in the synthesis of α-aryl-α-amino or α-aryl-β-amino acid derivatives. The method presented herein is a formal de-N,N-dialkylation of Sommelet–Hauser rearrang...

A new protecting group, 1,2-dimethoxy-4,5-dimethylene, for acyclic amino acid derivatives could be introduced by N,N-dialkylation with 1,2-bis(bromomethyl)-4,5-dimethoxybenzene (1) and removed via amine de-alkylation with acyl chlorides. The method can be used with base-induced [2,3] and [1,2] Stevens rearrangement products.

We developed a metalloporphyrin-based molecular container capped with a calix[4]arene, and its rigid cavity distinguished the slight structural differences in the aromatic guests.

Asymmetric α-2-tosylethenylation of (S)-2-(pyrrolidin-1-yl)propanoic acid esters was shown to produce good yields with high enantioselectivities. The reaction proceeds via the formation of a non-racemic ammonium enolate without an external source of chirality.

Asymmetric α-2-tosylvinylation of N-substituted proline esters using ethynyl tolyl sulfone as an electrophile was shown to proceed in good yield with high enantioselectivities without the addition of any bases. The reaction proceeds via the formation of N-2-tosylvinyl ammonium ylides.

The intermolecular aromatic substitution of N,N-disubstituted anilines with diazo esters is achieved under mild conditions in the presence of a catalytic amount of copper(II) triflate (up to 89 % yield). The scope and limitations regarding substrates, diazo esters, and ligands in this reaction are described. The intermolecular aromatic substitution...

Aza-Prins cyclization reaction of N-tosyl-3-butenylamine with aliphatic and aromatic aldehydes was performed using a combination of FeCl3 and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) or 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl4) in benzotrifluoride (BTF). The desired N-tosyl-4-chloro-2-substituted piperidines were o...

The tether-assisted synthesis of [3]rotaxane by olefin metathesis has been studied in detail. Bis(crown ether)s, in which two crown ethers are connected by a linker, were threaded onto ammonium salts bearing a terminal olefin to form pseudorotaxanes. The pseudorotaxanes were converted into tethered rotaxanes in the presence of Grubbs catalyst, foll...

A solution of potassium tert-butoxide in THF was shown to remarkably enhance the base-induced Sommelet–Hauser rearrangement of N-benzylic amino acid-derived ammonium ylides.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

"Chemical Equation Presented" Deuteration leads to stronger binding: Deuterated guests bind within the confined space of the molecular capsule more preferentially than protiated guests (see scheme). The van 't Hoff analysis of the competitive association reveals that the preferential binding of the deuterated guests is driven by enthalpy and oppose...

The tether-assisted synthesis of [3]rotaxane by olefin metathesis is described. The bis(crown ether)s, in which two crown ethers are connected by a linker, were converted to tethered rotaxanes, followed by removal of the linkers to produce [3]rotaxane. The biscrown structures promoted the formation of the tethered rotaxane, resulting in a notable i...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The synthesis of calix[4]arene-based molecular containers 1 and 2 along with the thermodynamic behaviors of cation binding are reported. The containers encapsulated N-methylpicolinium salts to form 1:1 host–guest complexes in chloroform. The thermodynamic investigations of the containers provide contrastive pictures for the process of their guest e...

Several models for the porphyrin ring current effect are constructed based on a classical line current approximation and their performances in reproducing the observed induced shifts of ligand protons in SnIV(porphyrin) dicarboxylate complexes are compared. A new model is selected and it is found that the diamagnetic ring current running on the inn...

A molecular container composed of monodeoxy-calix[4]arene and calix[4]arene is synthesized. The host binds planar cationic guests. The deoxy-aromatic ring acts as an open door when the guest is absent and closes on guest binding.

Calix[5]arene-based artificial receptor 1 capped with chiral macrocycle 6 was synthesized and showed strong binding towards ethyltrimethylammonium derivatives via cation/π and/or hydrogen bonding interactions. The calix[5]arene cavity provided the dissymmetric guest-binding environment in which chiral guests 9–19 were encapsulated in an enantiosele...

Molecular tweezers 1b having two alkyl thiol chains were prepared. Intramolecular cyclization of the thiols under oxidative conditions afforded tweezers 2b containing a disulfide bond. X-ray crystal analysis and temperature dependent 1H NMR spectra analysis revealed that the structure of 1b has a stepped anti arrangement of the three aromatic rings...

Two new halogenated briarane diterpenes, (-)-2-deacetyljunceellin (1) and (-)-3-deacetyljunceellin (2), and five known diterpenoids, junceellin, praelolide, junceellolide A, B, and D were isolated from the Papuan gorgonian coral Junceella fragilis. The structures of the new metabolites were determined by extensive 2D NMR experiments and by chemical...

Conformational analyses of flexible compounds with a chemical shift simulation method are described. It is known that NMR chemical shifts reflect the molecular structure, and hence, our method of analysis utilizes chemical shifts. Our newly developed chemical shift simulation method together with molecular dynamic calculation succeeded in the confo...

A new simple model of porphyrin ring current effect was proposed based on a line current approximation. It can reproduce the porphyrin-induced shifts for several Sn(IV)(tpp) and Sn(IV)(oep) dicarboxylate complexes quite satisfactorily. Perpendicular arrangement of the aromatic rings in the diaromatic-carboxylate complexes of Sn(IV)(tpp) and Sn(IV)(...

A new chiral carboxylic acid 1 was synthesized for determination of absolute configuration of secondary alcohols. Several chiral alcohols were converted to esters with 1. Their experimental esterification shift changes were successfully reproduced by the chemical shift simulation method combined with molecular dynamic simulation.

Five new sulfur-containing polybrominated bisindole (1∼5) wereisolated from the red alga, Laurencia brongniartii, in addition to six related compounds (6∼11), which have been previously found in the Okinawan alga. The structures of these new bisindole metabolites were elucidated on the basis of spectroscopic studies, as well as X-Ray crystallograph...

The synthesis of new flexible molecular tweezers based on 3,4,8,10,11,13-hexahydro-1H,6H-2,5,9,12-tetraoxa-benzo[1,2:4,5]dicyclooctene bearing two naphthalenes is presented. Intramolecular CH/π interaction between the alkyl ring and the two terminal naphthalenes controls the conformation to give a self-quenched cleft form.

4-Thia-5α- and 4-thia-5β-androstan-17-ones (1a and 1b) were synthesized in order to obtain the NMR shielding parameters for the thioether C–S bond. The complete NMR assignment of both the proton and carbon atoms for these compounds and substituent-induced shifts (SIS) from the corresponding androstanones (2a and 2b) are presented. A combination of...

Conformational analysis of dinaphthalene-1-carboxylatecomplex of SnIV(tpp) (1) in solution was carried out using temperature dependent 1H NMR spectra and chemical shift simulation method. It was found that two vertical conformers are in equilibrium in solution for 1.

A new simple model of porphyrin ring current effect was proposed based on a line current approximation. It can reproduce the porphyrin-induced shifts for some Sn(IV)(tpp) dicarboxylate complexes quite satisfactorily.

Synthesis of new flexible molecular tweezers 1·M 2 (M = 2H, Co, Zn, Cu, Ni) based on bis-dioxa[2.2]orthocyclophane bearing two porphyrins is presented. The molecular tweezers (1·(2H) 2) can bind not only planar π-electron acceptors, such as tetracyanoquinodimethane (TCNQ) and tetracyanobenzene (TCNB) but also a spherical guest C 60.

4-Aza-5α-androstanone(1α) and 4-aza-5β-androstanone(1β) were synthesized in order to obtain the NMR shielding parameters for the secondary amine group. A combination of the electric field effect and the anisotropy of the magnetic susceptibility of the CN bond can successfully reproduce the observed SIS values for these androstanes. Drastic chemica...

[3]Catenane 5a and 5b were synthesized conveniently by olefin metathesis dimerization of pseudorotaxanes 3a and 3b. The yields of 5a and 5b were influenced by concentrations of 3a and 3b, and a ring size of a center wheel of [3]catenane.

The synthesis and binding behavior of a Zn(II)–porphyrin having a calix[5]arene cap are presented. In order to synthesize such a bridged porphyrin, 5,15-bis(7-carboxy-1-naphthyl)-10,20-diphenylporphyrin having the syn arrangement of two naphthalene rings has been prepared. Amidation of the porphyrin and calix[5]arene having two amino functions and...

Structure elucidation of the inclusion complexes of monodeoxycalix[4]arene with small organic guests was carried out by X-ray crystallographic analysis and molecular dynamic simulation. Although the guest moves rapidly in the host cavity, the time averaged structure resembles the one obtained by the X-ray crystallography. Chemical shift simulation...

Conformational analysis of 1,4,11,14-tetraoxa[4.4]metacyclophane was carried out using a combination of the molecular mechanics calculation, analysis of the temperature dependent 1H NMR signal change and the chemical shift simulation method. The molecular mechanics calculation with Amber* force-field gave the two structures, one is highly symmetric...

Dihydro-dibenzophenanthrene derivatives 1a (1b) were synthesised in order to obtain the NMR shielding parameters for naphthalene ring. The 1H NMR assignment of 1a and substituent-induced shifts (SIS) from the corresponding androstanone ethylene ketal (2) are presented. A simple sum of the magnetic shielding of benzene rings can satisfactorily repro...

Thermodynamic parameters for the supramolecular complex formation of fullerene C60 with calix[5]arene receptors are reported. The entropy change in chloroform is negative, but in toluene is positive, suggesting the tight solvation around the guest in toluene. Desolvation of the guest plays an important role in the supramolecular complex formation i...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Syntheses of the proposed structure of periplanone J (1) and its epimer 2, and the discussion on the true structure of PJ based on the spectral study of 1,2 and the natural PJ are described.

Cyanohydrin ethers are the structural elements required for intramolecular alkylation to give the eight-membered taxoid B ring. This was demonstrated both for aromatic as well as for nonaromatic C rings (see below). EE = ethoxyethyl.

Cyanhydrinether sind die Strukturelemente , über die die Bildung des achtgliedrigen Taxoid‐B‐Rings durch intramolekulare Alkylierung gelingt. Dies wurde sowohl für aromatische als auch für nichtaromatische C‐Ringe (siehe unten) gezeigt. magnified image

Syntheses of the A-ring and the chiral C-ring model of taxol by using the intramolecular nitrile oxide cycloaddition and its diastereoselectivity based on MM2 transition state model are described. © 1997 Elsevier Science Ltd.

The stereoselective synthesis of a taxol intermediate via a biomimetic route is described. Aldol condensation of γ‐butyrolactone and citral derivatives generated three stereogenic centers at positions C1, C2, and C11 corresponding to taxol. Intramolecular alkylation of the cyanohydrin ether efficiently formed the 12‐membered ring system in which st...