Haruro Ishitani

Catalytic asymmetric aza Diels-Alder reactions using a chiral lanthanide Lewis acid. Enantioselective synthesis of tetrahydroquinoline derivatives using a catalytic amount of a chiral source

Abstract In the presence of a catalytic amount of the chiral ytterbium Lewis acid, which was prepared from Yb(OTf) 3 , (R)-(+)-BINOL, diazabicyclo[5.4.0]undec-7-ene (DBU), and an additive, achiral imines reacted with achiral dienophiles to afford the corresponding tetrahydroquinoline derivatives in high yields with high diastereo- and enantioselectivities. This is the first example of aza Diels-Alder reactions using a catalytic amount of a chiral source.

Scandium trifluoromethanesulfonate (Sc(OTf)3). A novel reusable catalyst in the Diels-Alder reaction

Scandium trifluoromethanesulfonate (Sc(OTf)3) is found to be quite effective as a Lewis acid catalyst in the Diels-Alder reaction. The novel catalyst is available in both aqueous and organic media, is easily recovered from aqueous layer after the reaction is completed, and can be reused.

Catalytic, Enantioselective Synthesis ofα-Aminonitriles with a Novel Zirconium Catalyst

Strecker reactions of aldimines with Bu3 SnCN in the presence of the novel chiral zirconium binuclear catalyst 1 provide α-aminonitriles in good yields and with high enantioselectivities. The reaction can be applied to a wide range of substrates. Since both enantiomers of the chiral sources are readily avaibable, both enantiomers of the α-aminonitriles are easily prepared according to this method. L=N-methylimidazole.

Lanthanide trifluoromethanesulfonates as reusable catalysts. Michael and Diels-Alder reactions

Abstract The Michael reaction of silyl enolates with α,β-unsaturated ketones and the Diels-Alder reaction of carbonyl containing dienophiles are catalyzed by a catalytic amount of lanthanide trifluoromethansulfonate to give the corresponding adducts in high yields. In both reactions, the catalyst can be recovered and reused.

Catalytic asymmetric synthesis of febrifugine and isofebrifugine

Abstract Antimalarial alkaloids, febrifugine (1) and isofebrifugine (2), were synthesized from simple achiral starting materials using tin(II)-catalyzed catalytic asymmetric aldol reaction and lanthanide-catalyzed aqueous three-component reaction as the key steps. These unambiguous total syntheses revealed that the absolute configurations of febrifugine and isofebrifugine were not (2′S, 3′R) and (2′R, 3′R) as reported previously but (2′R, 3′S) and (2′S, 3′S), respectively.

Asymmetric Diels-Alder reactions catalyzed by chiral lanthanide(III) trifluoromethanesulfonates. Unique structure of the triflate and stereoselective synthesis of both enantiomers using a single chiral source and a choice of achiral ligands

Abstract Chiral lanthanide trifluoromethanesulfonates (triflates) were developed and the unique structure of the triflates was revealed. In the presence of a catalytic amount of the triflate, acyl-1,3-oxazolidin-2-ones reacted with cyclopentadiene to afford the Diels-Alder adducts in high yields and with high enantiomeric excesses. According to the reactions, both enantiomers of the Diels-Alder adducts were stereoselectively prepared by using a single chiral source, R-(+)-binaphthol, and a choice of achiral ligands. When 3-acetyl-1,3-oxazolidin-2-one was combined with the original catalyst system consisting of lanthanide triflate, R-(+)-binaphthol, and cis-1,2,6-trimethylpiperidine, a new catalyst was generated (catalyst A). In the presence of this catalyst, 3-acyl-1,3-oxazolidin-2-ones reacted with cyclopentadiene to afford the endo adducts in high enantiomeric excesses. The absolute configuration of the products was 2S, 3R. On the other hand, when 3-phenylacetylacetone (PAA) was mixed with the original catalyst system (catalyst B), reverse enantiofacial selectivities were observed and endo adducts with the absolute configuration 2R, 3S were obtained in high enantiomeric excesses.

Asymmetric Diels-Alder reaction catalyzed by a chiral ytterbium trifluoromethanesulfonate

Abstract In the presence of a catalytic amount of chiral ytterbium trifluoromethanesulfonate (triflate), acyl-1,3-oxazolidin-2-ones or methacrolein reacted with cyclopentadiene to afford the corresponding Diels-Alder adduct in high yields and with moderate to excellent enantiomeric excesses.

Characterization of chiral ytterbium and scandium catalysts based on their trifluoromethanesulfonates in asymmetric Diels-Alder reactions

Abstract The unique structure of chiral ytterbium and scandium catalysts (prepared from ytterbium or scandium trifluoromethanesulfonate, (R)-(+)-binaphthol, and a tertiary amine) was determined. The structure was characterized by hydrogen bonds between the phenolic hydrogens of (R)-(+)-binaphthol and the nitrogens of the tertiary amines. Aging and aggregation of the catalysts are also reported.

Lewis acid-mediated [3+2] cycloaddition between hydrazones and olefins

Abstract [3+2] Cycloaddition between hydrazones and olefins was accelerated in the presence of a stoichiometric amount of BF 3 ·OEt 2 or a catalytic amount of Zr(OTf) 4 , Hf(OTf) 4 , or Sc(OTf) 3 under mild conditions. The corresponding pyrazolidine derivatives were obtained in moderate to high yields using this novel [3+2] Lewis acid catalysis.

A novel Mannich-type reaction: Lanthanide triflate-catalyzed reactions of N-(α-aminoalkyl)benzotriazoles with silyl enolates

Abstract In the presence of a catalytic amount of a lanthanide triflate, N-(α-aminnoalkyl)benzotriazoles reacted with silyl enolates to give the corresponding β-amino ketone or ester derivatives in high yields with high diastereoselectivities.