Tomoshige Kobayashi

Dipolar Cycloadditions of Mesoionic Compounds with 2-tert-Butylfulvenes. A New Route to Pseudo-hetero-azulenes via Sterically Assisted [4π + 6π] Cycloadditions, and Isomerization of Adducts 1 ; 2

Abstract Several mesoionic compounds react with 2-tert-butylfulvene derivatives to form [4π + 6π] and/or [4π + 2π] cycloadducts. They undergo further fragmentation, elimination, or isomerization under the reaction conditions to give a variety of products including several condensed heterocycles which are isoelectronic with azulene. An oxazolium-4-olate, on contact with a small amount of air, was found to form a tricyclic oxygenated dimer.

A through-space interaction of 3-benzylthiothieno[3,4-b]indolizine derivatives combined by a highly flexible spacer

Some ethyl 1-benzoyl-3-[(un)substituted benzylthio]thieno[3,4-b]indolizine-9-carboxylates were prepared and their conformations were investigated. In the solid state and the chloroform solution they had stacked structuresin which the phenyl ring and the pyridine moiety of theino[3,4-b]indolizine ring are partly overlapped.

Enantioselective synthesis of a chiral pyridazinone derivative by lipase-catalyzed hydrolysis

The lipase-catalyzed resolution of 2-(acyloxymethyl)-4,5-dihydro-5-methylpyridazin-3(2H)-one derivatives in organic solvents containing water was demonstrated to be a practical method for the synthesis of a chiral pyridazinone bearing a pyrazolopyridine ring, which is a potent phosphodiesterase inhibitor.

Cyclovoltammetric Investigation into the Homoconjugation of Plural Pyrazine Rings Linked by Bicyclo[2.2.2]octadiene Spacers

The synthesis and cyclovoltammetric investigation of the ethano-bridged pyrazinoquinoxalines 2−4 and the bridged polyazapolyacenes 25−27 are described. A large difference between the first and the second reduction potentials for 2−4 indicated the presence of strong homoconjugation between the two spatially separated pyrazine rings. The bridged polyazapolyacenes 25−27, on the other hand − with the exception of 27 − exhibited four reduction peaks and the reversibility was found to be poor when compared with that of 2−4. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A New Molecular Receptor Based on Thiophene Congener of Troger's Base: Selective Binding with Aliphatic and Aromatic Dicarboxylic Acids

A new molecular receptor bearing pyridylamino groups was prepared with a thiophene congener of Trogers base as a spacer, and was found to exhibit selective binding toward aliphatic and aromatic dicarboxylic acids, primarily depending on the length of the carbon chain.

Dipolar cycloaddtions of several mesoionic compounds with tert-butylfulvene derivatives; versatile reactions, sterically controlled [4π+ 6π] cycloadditions and a new route to heterocycles isoelectronic with azulene

Several mesoionic compounds react with 2-tert-butylfulvene derivatives to form [4π+ 2π] and [4π+ 6π] cycloadducts, which under the reaction conditions, undergo further fragmentation, elimination, or isomerization giving a variety of products including several condensed heterocycles which are isoelectronic with azulene.

Metal-carbonyl-induced reaction of isoxazoles. Ring cleavage and reduction by hexacarbonylmolybdenum, pentacarbonyliron, or nonacarbonyldi-iron

In the presence of [Mo(CO)6] and water the isoxazoles (1a–f) undergo thermally induced reductive cleavage of the N–O bond to give β-amino enones in good yield. Similar results were obtained by the use of [Fe(CO)5] and water with photoirradiation, or of [Fe2(CO)9] and water with heating. A mechanism involving an N-complexed isoxazolepentacarbonylmolybdenum or isoxazoletetracarbonyliron, and a [Mo(CO)5]- or [Fe(CO)4]-complexed (β-oxo vinyl)nitrene intermediate is proposed for the reactions. The complexed nitrene moiety could be reduced by the central metal in the presence of water to give amine. Furthermore, treatment of 2-benzoyl-3-phenyl-2H-azirine (8a), which is an isomer of 3,5-diphenylisoxazole, with the metal carbonyls and water also resulted in the formation of a β-amino enone possibly via the corresponding complexed (β-oxo vinyl)nitrene. An N-complexed isoxazolepentacarbonylmolybdenum intermediate was prepared by the photoreaction of [Mo(CO)6] with 3,5-dimethylisoxazoie. Its characterization, and chemical transformations, have been carried out to investigate the proposed mechanism.

Swern Oxidation of Bicyclo(2.2.1)hept-5-ene-2,3-diol and Its Pyrazine-fused Derivatives: An Improved Synthesis of Bicyclo(2.2.1)hept-5-ene-2,3-dione and An Unexpected Ring- Opening Reaction

An improved synthesis of bicyclo[2.2.1]hept-5-ene-2,3-dione by Swern oxidation of bicyclo[2.2.1]hept-5-ene-2,3-diol, and an unexpected ring-opening reaction by the Swern oxidation of pyrazine-fused congeners are described.

Neighboring effect by heteroaromatic rings: formation of skeletally rearranged adducts by cycloaddition reaction of norbornadiene-fused pyridazines and pyrazines with 4-phenyl-1,2,4-triazole-3,5(4H)-dione

Abstract Norbornadiene-fused pyridazines and pyrazines reacted with 4-phenyl-1, 2,4-triazole-3,5(4 H )-dione to give skeletally rearranged adducts in moderate yields. A similar reaction with fused pyridazine N -oxides or a fused pyrazine N -oxide resulted in the regioselective formation of the rearranged adduct. The formations of the skeletally rearranged adducts would be ascribed to the intervention of bridged heteroarenium ion intermediates formed by the neighboring group participation of heteroaromatic rings.

Neighboring group effect of five-membered heteroaromatic rings for π-facial selectivity in the reactions of fused isopropylidenenorbornene systems with electrophilic reagents

Abstract The electrophilic reactions of novel isopropylidenenorbornadienes and isopropylidenenorbornenes fused with a furan, pyrrole, thiophene, and pyrazole ring with 1,2,4-triazole-3,5-(4H)-dione, m-chloroperbenzoic acid, dichlorocarbene, and N-bromosuccinimide (NBS) indicated that the neighboring group effect of the five-membered heteroaromatic rings was, unexpectedly, almost similar to that of a benzene ring except for the reaction with NBS.