Hidetoshi Yamamoto

C2-symmetric 1,2-diamine/copper(II) trifluoromethanesulfonate complexes as chiral catalysts. Asymmetric cyclopropanations of styrene with diazo esters

Abstract Styrene and diazo esters react in the presence of copper(II) trifluoromethanesulfonate (1 mol%) and (1S,2S)-N,N′-di(mesitylmethyl)-1,2-diphenyl-1,2-ethanediamine (2 – 3 mol%) to give 2-phenyl-1-cyclopropanecarboxylates in good to excellent optical yields. This reaction has been applied tov the synthesis of chrythanthemic acid.

Metal ion-mediated diastereoface-selective nitrone cycloadditions. Reaction mechanism for the reversal of regloselectivity observed in the magnesium and zinc ion-mediated nitrone cycloadditions of allylic alcohols

Magnesium and zinc ion-mediated cycloaddition reactions of a carbonyl-conjugated nitrone, (Z)-N-(benzoylmethylene)aniline N-oxide to the allylic alcohols bearing a chirality at α-position give isoxazolidine-5-alcohol and isoxazolidine-4-alcohol derivatives, respectively, both in highly lk-1,2-inductive manners. α,α-Disubstitution of allylic alcohol dipolarophiles virtually inhibits the zinc ion-catalyzed reaction paths, and use of a coordinating solvent in the magnesium ion-catalyzed reactions leads to the reversal of regioselectivity. Reaction mechanism for the metal ion-catalyzed competitive cycloadditions is proposed.

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.

Metal ion-mediated diastereoface-selective 1,3-dipolar cycloaddition of nitrile oxides with dipolarophiles bearing an oxazolidinone chiral auxiliary

Abstract Magnesium ion-mediated cycloaddition reactions of nitrile oxides to chiral 3-acryloyl-2-oxazolidinones lead to highly diastereoselective formation of 2-isoxazolines. The magnesium ion serves to fix the α,β-unsaturated moiety through chelation to effect chiral shielding. These asymmetric reactions provide the first successful examples of Lewis acid-mediated stereocontrol of nitrile oxide cycloaddition reactions to electron-deficient dipolarophiles.

dl-selective reductive coupling/Dieckmann condensation sequence of α,β-unsaturated amides with samarium(II) iodide/HMPA. Synthesis of a new ligand, trans-1,2-cyclopentanediyl-2,2′-biphenol

Abstract By action of SmI 2 -HMPA in THF, the N , N -dimethyl derivatives of ( E )- α , β -unsaturated amides produce the 1,2- trans -2,3- trans stereoisomers of 2,3-disubstituted 5-oxo-1-cyclopentane-carboxamides via a highly dl -selective reductive coupling followed by Dieckmann condensation. Water- d 2 is an effective quenching agent. This reaction is successfully applied to the synthesis of trans -1,2-cyclopentanediyl-2,2′-biphenol, which is a new C 2 -symmetric chiral ligand.

Generation of NH-azomethine imine intermediates through the 1,2-hydrogen shift of hydrazones and their intermolecular cycloaddition reaction with olefinic dipolarophiles

The thermal 1,2-hydrogen shift of the hydrazone generates the NH-azomethine imine intermediate in the 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde system under mild conditions. Therein, the resulting NH-azomethine imine should be stabilized by forming an internal hydrogen bond with the carbonyl oxygen at the 4-position. Its smooth stereoselective intermolecular cycloaddition reaction with olefinic dipolarophiles giving pyrazolidine derivatives is discussed.

Reaction of 2-substituted-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde oximes with electron-deficient olefins and acetylenes

Abstract A facile oxime–nitrone isomerization through the 1,2-hydrogen shift in 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde oximes is discussed. The resultant NH-nitrones are trapped by maleimides to afford intermolecular cycloadducts. The reaction of the oximes with electron-deficient acetylenes undergoes via another path initiated by a nucleophilic attack of the oxime to acetylene moiety.

Catalytic efficiency, ligand acceleration, and concentration effect in magnesium ion mediated 1,3-dipolar cycloadditions of mesitonitrile oxide to allylic alcohols

Abstract Magnesium ion catalysis in nitrile oxide cycloadditions to allylic alcohols has been studied by use of stable mesitonitrile oxide. Moderate catalytic efficiency, ligand acceleration effect, and concentration effect have been observed to provide a promising access to a catalytic version of 1,3-dipolar cycloaddition reactions.

Stereoselective Azepine‐Ring Formation Through Ene Reactions of 3‐(Alk‐2‐enyl)amino‐2‐cyanoacrolein Derivatives

The reaction of 3-[N-(alk-2-enyl)benzylamino]-2-cyanoacroleins 9 with primary amines 12 and 13 gave 4,5-dihydro-1H-azepines 14 and 15 stereoselectively, through an intramolecular ene reaction of the imine derivatives of 9. Similarly, carbonyl-ene reaction of acrolein derivatives 9, and olefin-ene reaction of their conjugated diene compounds 22, and 24-27 are also discussed. These ene reactions established an efficient synthetic approach toward monocyclic azepine ring formation.

Stereoselective pyrroline-ring formation through the cyclization of conjugated azomethine ylides at the periphery of pyrido[1,2-a]pyrimidine system

The thermal reaction of N-benzyl-N-[3-(N-substituted imino)methyl-4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl]amino acid esters, generated from aldehyde esters and primary amines, provides 2,3-dihydropyrido[1,2-a]pyrrolo[2,3-d]pyrimidin-4(1H)-one derivatives effectively and stereoselectively. Therein, the stereoselective generation of conjugated azomethine ylides from the imine esters and their cyclization is essential for the pyrroline-ring formation.