Masaki Nishiuchi

Regiocontrol of nitrile oxide cycloadditions to allyl alcohols. Synthesis of 4-substituted and 4,4-disubstituted 5-hydroxymethyl-2-isoxazolines

Abstract The first regiocontrol of nitrile oxide cycloadditions is described. Reaction of benzonitrile oxide with (E)-2-butenol is highly accelerated by the presence of a magnesium alkoxide, and this reaction proceeds in an exclusively regioselective manner to produce 5-hydroxymethyl-4-methyl-3-phenyl-2-isoxazoline as the sole cycloadduct. Synthetic applications to other substituted allyl alcohols are discussed.

Generation of nitrile oxides through O-metalation of hydroximoyl chlorides. Chelation-controlled syn-selective cycloaddition of nitrile oxides to α-substituted allyl alcohols

Abstract New generation of nitrile oxides by treatment of hydroximoyl chlorides with organometallics is reported. Their cycloadditions to the allyl alcohols bearing a chiral center at the 1-position proceed in a syn-selective manner, providing the first example of stereocontrol of 1,3-dipolar cycloaddition by the aid of metal chelation.

Curious oxygen effect on photosensitized electron-transfer reactions of benzophenone oxime O-methyl ethers: one-way photoisomerization of an iminic double bond

Abstract Under an oxygen atmosphere, the E and Z isomer ratio of N -methoxy-4-methoxyphenyl-4′-methylphenylmethanimine (initially, [ E ]/[ Z ]=1/1) reached 4/96 upon irradiation (>360 nm) of 9,10-dicyanoanthracene (DCA) as a photosensitizer in acetonitrile.

A highly effective quenching method of 1,3-dipolar cycloadditions of nitrile oxides or nitrile oxide/Lewis acid complexes by use of 2-propenyloxymagnesium bromide

Abstract 2-Propenyloxymagnesium bromide, readily prepared by treating 2-propen-l-ol with EtMgBr, is a highly effective quencher of nitrile oxide cycloadditions since this alkoxide is much more reactive to nitrile oxides than any other ever known dipolarophiles of the electron-deficient, electron-rich, and strained types, including 3-buten-2-one, ethyl vinyl ether, and norbornene, respectively. This quencher is also effectively utilized to terminate the dipolar cycloadditions of nitrile oxide/Lewis acid complexes.

Regioisomeric allene dimer formation by the reaction of tetraarylbutatrienes with tetracyanoethene.

The reaction of tetraarylbutatrienes (tetraaryl[3]cumulenes) with tetracyanoethene (TCNE), a strong electron-accepting molecule, at room temperature yielded novel four-membered ring compounds (head-to-tail unsymmetrically substituted diarylallene dimers) by [2 + 2] cycloaddition of the central C=C bond of the butatrienes. This reaction proceeded through a head-to-head symmetrically substituted diarylallene dimer intermediate. Unsymmetrical butatriene also formed a small amount of another head-to-tail dimer. Although the allene dimer is stable in nonpolar solvents, it converts to other bicyclic and tricyclic compounds in MeOH or CH3CN at room temperature.

Facile synthesis of polyhydroxycoumaronochromones with quinones: synthesis of alkylpolyhydroxy- and alkoxycoumaronochromones from 2′-hydroxyisoflavones

Abstract 4′,5,7-Trihydroxy- or 8-alkyl-4′,5,7-trihydroxycoumaronochromones were synthesized by oxidative cyclization of the corresponding 2′-hydroxyisoflavones with o -chloranil under mild conditions. By contrast, alkoxycoumaronochromones were synthesized by oxidative cyclization of the corresponding 2′-hydroxyisoflavones with DDQ.

Regioselective Synthesis of Prenylisoflavones. Syntheses of Lupiwighteone, Lupiwighteone Hydrate and Related Compounds

Catalytic hydrogenation and the subsequent dehydration of 8-(3-hydroxy-3-methylbutynyl)isoflavone 12, which was synthesized by the palladium-catalyzed coupling reaction of 4′,5,7-tris(benzyloxy)-8-iodoisoflavone 11 with 2-methyl-3-butyn-2-ol, gave a mixture of 8-prenylisoflavone 16 and the isomer [5-acetoxy-8-(3-methyl-3-butenyl)isoflavone] 17, and after the separation of 16 was accomplished by treatment of the mixture with Hg(NO3)2, hydrolysis of 16 afforded 4′,5,7-trihydroxy-8-prenylisoflavone (lupiwighteone) 1.

Photoreactions of 1,3-Dipolar Cycloadducts of Mesoionic Compounds with Buckminsterfullerene

Cycloaddition reactions of buckminsterfullerene (C 60 ) with mesoionic compounds gave the 1 to 1 cycloadducts reacted at the 6-6 double bond of C 60 as a sole product. A thermal reaction of the adducts proceeded in a reversed fashion and another dienophile trapped the liberated mesoionic compounds. Thermogravimetric analyses of the adducts reveal that extrusion of small fragment occurs at controlled temperature. UV-VIS spectra of the adducts altered with isosbestic points upon irradiation of them. Preparative photoreaction gave only a black compound insoluble in major organic solvents.