Kuniaki Itoh

Synthesis of C-nucleosides from non-carbohydrate precursors. A 2,4-dioxoimidazolidin-5-yl ribofuranoside

Abstract 3-Phenyl-2,4-dioxoimidazolidin-5-yl ribofuranoside (a hydantoin C-riboside) was synthesized from a Diels-Alder adduct of furan with methyl nitroacrylate.

The Structure of 1,3-Enaminoketonatoboron Difluorides in Solution and in the Solid State

Nuclear magnetic resonance, infrared, and ultraviolet spectra and X-ray analysis of three 1,3-enaminoketonatoboron difluorides (BF2 complexes, (2a)–(2c)) both in solution and in the solid state have been recorded. Their structures are discussed in relation to the electron distribution in their chelate rings and in comparison with those of their parent compounds (1a)–(1c) and 1,3-diketonatoboron difluorides. C1 and C3 chemical shifts in the 13C NMR spectra indicated that the ketoamine and enolimine tautomeric forms may be present in equal amounts. Additionally, the phenyl groups participate in the delocalized π-electron system of the chelate ring. On the other hand, in the solid state, a comparison of the bond lengths by X-ray analysis provides information on processes occurring as contribution of the enolimine form increases. The information found may offer valuable suggestions for the reactivity and the structure of the products for the reactions of the BF2 complexes.

Photodimerization of enaminoketonatoboron difluorides

Irradiation of enaminoketonatoboron difluorides (complexes) in solution in the presence of benzophenone gave two stereoisomeric dimers: syn head-to-tail (H-T) and anti H-T. The observed stereochemical control can be understood on the basis of steric energies calculated by molecular mechanics. However, in the crystalline state the complexes selectively afforded an anti H-T dimer. X-Ray analysis of the complex confirms that this reaction proceeds according to known topochemical principles. The cyclobutane ring formed shows planar and puckered forms in the syn H-T and anti H-T dimers, respectively.

Photocycloaddition of 1,3-Diphenyl-N-methyl Enaminoketonatoboron Difluoride with Simple Olefins

The photoaddition of some cyclic and acyclic olefins to (N-B)-Z-1-difluoroboryloxy-1,3-diphenyl-3-methylimino-1-propene (BF 2 -complex (1)) is discussed. Some of the resulting [2+2] photoadducts produce cyclobutane derivatives having cis configurations. The rearrangements of the cyclobutanes give pyridinium salts and 1,5-diketones. Reaction schemes for the formation of the cyclobutanes are presented. The dimer of the BF 2 -complex (1) is also formed in a reaction which is in competition with the olefins photoaddition.

The reaction of β-nitrostyrenes with 2-methoxyfuran: a novel formation of isoxazoline N-oxide together with Michael adducts

2-Methoxyfuran reacts with β-nitrostyrenes to give Michael adducts. Interestingly, isoxazoline N-oxides were obtained in the reactions with β-nitrostyrenes possessing additional electron-withdrawing groups (COPh and CO2Et).

Certain cinnamonitriles react with 2-methoxyfuran to produce a new phenylcyclopropane product

2-Methoxyfuran as a diene fails to generate a Diels-Alder adduct when it reacts with β-cyanostyrenes (cinnamonitriles). However, in the reaction with β-cyanostyrenes possessing additional electron-withdrawing groups (CN, CO 2 Et, SO 2 Ph and COPh), it yielded two new phenylcyclopropanes. The formation of the cyclopropane ring may occur through the opening of the furan ring in the β-cyanostyrene-furan complex (zwitterion) formed. The product formation process involves a sterically controlled intramolecular reaction.

Novel formation of isoxazoline N-oxide in addition to Michael adduct from the reaction of β-nitrostyrenes with 2―methoxyfuran ― Experimental and theoretical studies

2-Methoxyfuran reacts with β-nitrostyrenes to give Michael adducts. Interestingly, isoxazoline N-oxides were obtained in the reactions with β-nitrostyrenes possessing additional electron-withdrawing groups [COPh (2f) and CO2Et (2g)]. (Z)-Nitrostyrene (2g) gives trans-isoxazoline (4g) and (E)-nitrostyrene (2f) leads to the cis-form product 4f. We have used theoretical methods to investigate the mechanism and to probe the regio- and stereo-selectivity observed in the rearrangement and the Michael reactions. To account for the selectivity observed in these reactions, we examined the Fukui functions and located the transition states (TS) using density functional theory (DFT) calculations at the B3LYP/6–31G* level. The first step involves a nucleophilic attack by the α-carbon atom (C4) of the furan ring on the vinyl C-atom (C5) of the nitrostyrene part to give a zwitterionic intermediate (IN1). Fission of the C–O bond of the furan ring in the intermediate and ring closure via the oxygen atom (endo-O atom) of t...

1-Difluoroboronyloxy-3-(N-methylimino)-1-phenyl-1-butene and its two photoproducts

The title compound, C 11 H 12 BF 2 NO, was found to be converted by irradiation to the anti and syn head-to-tail dimers {1,3.-bis(difluoroboronyloxy)-2,4-bis[1-(N-methylimino)ethyl]-1,3-diphenylcyclobutane, C 22 H 24 B 2 F 4 N 2 O 2 }. The enaminoketone group of each complex takes a ring structure chelated through the BF 2 group.

The photoaddition of enaminoketonatoboron difluorides with trans-stilbene

The photochemical reactions of enaminoketonatoboron diflurides 1 with trans-stilbene gives cyclobutanes 2 and azetidines 3 in a regio- and stereo-specific manner.

Cycloaddition of 1-Methoxy-3-trimethylsilyloxybutadiene with Halogenated Carbonyl Compounds

Cycloadditions of 1-methoxy-3-trimethylsilyloxy-1,3-butadiene (1) with halogenated carbonyl compounds (2) yielded corresponding substituted tetrahydro- and/or dihydropyran-4-ones (3 and/or 4). Lewis acids were found to be effective as catalysts. Reactions with less reactive carbonyl compounds (2c,d) afforded p-hydroxyacetophenone (5) produced by cyclodimerization of 1. Stereochemistry of the adducts was deduced by 1 H nmr spectroscopy