Koichi Narasaka

Stereoselective reduction of β hydroxyketones to 1,3-diols highly selective 1,3-asymmetric induction via boron chelates

Abstract Highly selective asymmetric induction can be achieved in the reduction of acyclic β-hydroxyketones via boron chelates. Treatment of β-hydroxyketones ( 1 ) with tributyl or tri-isobutylborane and successively with sodium borohydride afforded syn -1,3-diols ( 3 ) in highly stereo-selective manner, Syn -α-substituted-β -hydroxyketones ( 8 ) were also reduced to give syn , syn -1,3-diols ( 9 ) exclusively. The reaction was further applied to the convenient preparation of 3-deoxy-hexoses.

Mn(III)-Catalyzed Synthesis of Pyrroles from Vinyl Azides and 1,3-Dicarbonyl Compounds

Polysubstituted N-H pyrroles with a wide variety of substituents were prepared from vinyl azides and 1,3-dicarbonyl compounds by using Mn(III) complexes as catalysts.

The rhodium-catalyzed Pauson–Khand reaction

Abstract A rhodium carbonyl complex, [RhCl(CO)2]2, serves as a catalyst of the intra- and inter-molecular Pauson–Khand reaction. By the use of the rhodium catalyst, cyclopentenone derivatives are prepared from various 1,6- and 1,7-enynes under 1 atm of CO. Furthermore, this rhodium-catalyzed reaction is accelerated by reducing partial pressure of CO to less than 1 atm.

Synthesis of (-)-sordarin.

The first total synthesis of (-)-sordarin (1) was accomplished exploiting the following key reactions: (i) Ag(I)-catalyzed oxidative radical cyclization of a cyclopropanol derivative leading to a bicyclo[5.3.0]decan-3-one skeleton; (ii) Pd(0)-catalyzed intramolecular allylation reaction resulting in the entire strained bicyclo[2.2.1]heptan-2-one framework of sordaricin (2); (iii) selective dihydroxylation of terminal alkenes by the combined use of OsO(4) and PhB(OH)(2); and (iv) beta(1,2-cis)-selective glycosidation via a 1,3-anchimeric assistance from a 4-methoxybenzoyl group.

Use of 1,3-oxazolidin-2-one derivatives of 3-borylpropenoic acids as β-hydroxy acrylic acid equivalents in the asymmetric Diels-Alder reaction catalyzed by a chiral titanium reagent

Abstract Catalytic asymmetric Diels-Alder reaction was developed by employing 3-(3-boryl-propenoyl)-1,3-oxazolidin-2-one as a β-hydroxyacrylic acid equivalent. With a catalytic amount of the titanium reagent, 3-(3-borylpropenoyl)-1,3-oxazolidin-2-ones react smoothly with various dienes in the presence of Molecular Sieves 4A to afford the adducts in high yield with high optical purity. Boryl groups of the adducts were converted to hydroxyl group oxidatively.

Synthesis of azaheterocycles from oxime derivatives

Electrophilic amination of Grignard reagents has been accomplished by using O-sulfonyloximes as amination reagents. Benzophenone O-sulfonyloxime derivatives react with Grignard reagents on sp2 nitrogen, yielding primary amines by successive hydrolysis of the resulting N-alkylimines. Various cyclic imines are synthesized by Pd-catalyzed reaction from olefinic oxime derivatives. That is, treatment of O-pentafluorobenzoyloximes of olefinic ketones with a catalytic amount of Pd(PPh3)4 and triethylamine affords nitrogen-containing heterocycles, such as pyrroles, pyridines, isoquinolines, spiro-imines, and aza-azulenes. This reaction proceeds via the initial formation of alkylideneaminopalladium(II) species generated by oxidative addition of the oximes to the Pd(0) complex, and the following intramolecular amination on the olefinic moiety. Cyclic imines are prepared from γ,δ-unsaturated O-acetyloximes by treatment with acetic acid and 1,4-cyclohexadiene in the presence of a catalytic amount of 1,5-naphthalene-diol. γ,δ-Unsaturated ketone O-methoxycarbonyloximes are transformed to 2-bromomethyl-3,4 dihydro-2H-pyrroles by the action of a catalytic amount of Cu(I) bromide dimethyl sulfide complex and lithium bromide.

Asymmetric synthesis of the hydronaphthalene moieties of mevinic acids

Abstract The hydronaphthalene moieties of mevinic acids are synthesized enantioselectively by using the asymmetric intramolecular Diels-Alder reaction catalyzed by a chiral titanium reagent.

Metal-assisted amination with oxime derivatives

Electrophilic amination of Grignard reagents is accomplished by using O-sulfonyl-oximes of benzophenone derivatives. In the presence of a catalytic amount of CuCN, O-sulfonyloxime of 4,4¢-bis(trifluoromethyl)benzophenone reacts with alkyl Grignard reagents in tetrahydrofuran (THF) and hexamethylphosphoramide (HMPA), yielding primary alkyl-amines by successive hydrolysis of the resulting N-alkylimines. Arylamines are also prepared as well as alkylamines by treating O-sulfonyloxime of 3,3¢,5,5¢-tetrakis(trifluoromethyl)benzophenone in toluene-ether with Grignard reagents. Various cyclic imines are synthesized by palladium-catalyzed cyclization of olefinic oxime derivatives. That is, the reaction of O-pentafluorobenzoyloximes of olefinic ketones with a catalytic amount of Pd(PPh3)4 and triethylamine in dimethylformamide (DMF) affords nitrogen-containing heterocycles, such as pyrroles, pyridines, isoquinolines, spiro-imines, and aza-azulenes. This reaction proceeds via the initial formation of alkylideneaminopalladium species generated by oxidative addition of oximes to Pd(0), and the successive intramolecular Heck-type amination occurs on the olefinic moiety.

Synthesis of dihydropyrroles by the intramolecular addition of alkylideneaminyl radicals generated from O-2,4-dinitrophenyloximes of γ,δ-unsaturated ketones

Abstract Alkylideneaminyl radicals are generated from O -2,4-dinitrophenyloximes of γ,δ-unsaturated ketones by treatment with NaH and 3,4-methylenedioxyphenol. The resulting radical species successively add to the olefinic moiety intramolecularly to afford dihydropyrroles in the presence of a radical trapping agent. This method is applied for the stereoselective synthesis of xenovenine, a bicyclic 3,5-dialkylpyrrolizidine alkaloid.

Asymmetric synthesis of methylenecyclobutanes and their transformation to medium-sized carbocyclic compounds

Abstract The catalytic asymmetric [2+2] cycloaddition proceeds between 3-(2-alkenoyl)-1, 3-oxazolidin-2-ones and 1, 2-propadienyl sulfides having various substituents at 1-position, affording methylenecyclobutane derivatives with high optical purity. Seven and eight membered carbocycles with chiral side chains are prepared by the ring cleavage reaction and successive cationic cyclization of the chiral methylenecyclobutane derivatives having ω-alkenyl substituents.