Seiji Niwa

Chiral piperazine as a new chiral catalyst for the enantioselective addition of dialkyl zincs to aryl aldehydes

Abstract Optically active sec -alcohols in 90% enantiomeric excess were obtained from the enantioselective addition of dialkyl zincs to aryl aldehydes in the presence of a catalytic amount of dilithium salt of (2 S , 5 S )-2, 5-diisopropylpiperazine.

Asymmetric self-catalytic reaction. Self-production of chiral 1-(3-pyridyl)alkanols as chiral self-catalysts in the enantioselective addition of dialkylzinc reagents to pyridine-3-carbaldehyde

Optically active 1-(3-pyridyl)alkanols, chiral self-catalysts, produced themselves of the same configuration in the enantioselective addition of dialkylzinc reagents to pyridine-3-carbaldehyde.

Enantioselective addition of dialkylzincs to pyridine-carbaldehyde in the presence of chiral aminoalcohols asymmetric synthesis of pyridylalkyl alcohols

1-(3-Pyridyl) ethanol and -propanol were synthesized in moderate to good enantiomeric excesses by the enantioselective addition of dialkylzincs to nicotinaldehyde using N,N-dibutylnorephedrine as chiral catalyst

Catalytic asymmetric synthesis of optically active alkynyl alcohols by enantioselective alkynylation of aldehydes and by enantioselective alkylation of alkynyl aldehydes

Catalytic asymmetric synthesis of optically active secondary alkynyl alcohols (1) by enantioselective addition of organozinc reagents to aldehydes in the presence of a small amount of catalyst was examined. Enantioselective alkynylation of benzaldehyde by alkynylzinc reagents using (1S,2R)-(–)-N,N-dibutylnorephedrine (2c) as a chiral catalyst gave (1) in moderate enantiomeric excess (e.e.). On the other hand, enantioselective addition of dialkylzinc reagents to alkynyl aldehydes using (S)-(+)-(1-methylpyrrolidin-2-yl)diphenylmethanol (3) as a chiral catalyst afforded (1) in high e.e. The reaction of 3-trimethylsilylprop-2-ynal with diethylzinc in toluene at –20 °C using (S)-(+)-(3)(5 mol%) afforded (–)-1-trimethylsilylpent-1-yn-3-ol in 78% e.e. (S)-(–)-Oct-1-yn-3-ol (6)(precursor of the prostaglandin side chain) was also synthesized in 69% e.e. by employing dipentylzinc.

Catalytic Asymmetric Synthesis of 2- and 3-Furylcarbinols

Optically active 2- and 3-furylcarbinols were synthesized in high enantiomeric excesses by the enantioselective addition of dialkylzinc reagents to 2- or 3-furaldehydes using N,N-dibutylnorephedrine and (S)-diphenyl (1-methylpyrrolidin-2-yl) methanol as chiral catalysts

Asymmetric synthesis of 2-aryl substituted oxetanes by enantioselective reduction of β-halogenoketones using lithium borohydride modified with N,N′-dibenzoylcystine

Optically active 2-aryl substituted oxetanes are synthesised in high enantiomeric excesses (up to 89% e.e.)via enantioselective reduction of β-halogenoketones with lithium borohydride using (R,R′)-N,N′-dibenzoylcystine and t-butyl alcohol as ligands.

Asymmetric synthesis of optically active fluorine-containing alcohols using chiral catalysts

Abstract Optically active fluorine-containing alcohols have been synthesized in high enantiomeric excess by the catalytic enantioselective addition of dialkylzincs to fluorine-containing aldehydes.

Asymmetric synthesis of alcohols with two chiral centres from a racemic aldehyde by the selective addition of dialkylzinc reagents using (1S,2R)-(–)-N,N-dibutylnorephedrine and (S)-(+)-diphenyl-(1-methylpyrrolidin-2-yl)methanol as chiral catalysts

Optically active alcohols with two chiral centres were obtained in up to 93% enantiomeric excess by the selective addition of dialkylzinc reagents to the racemic aldehyde, 2-phenylpropanal, using the title compounds as chiral catalysts.

Asymmetric synthesis of pyridylethanols and amino alcohols by enantioselective reduction with lithium borohydride modified with N,N′-dibenzoylcystine

Optically active 1-pyridylethanols and β- and γ-amino alcohols are obtained in high enantiomeric excess from the enantioselective reduction of acetylpyridines and amino ketones using lithium borohydride, N,N′-dibenzoylcystine, and ethanol.

Asymmetric synthesis using chiral piperazines. Part 3. Enantioselective addition of dialkylzincs to aryl aldehydes catalysed by chiral piperazines

The use of chiral piperazines (cyclic diamines) 1 as chiral catalysts for the enantioselective addition of dialkylzincs to aldehydes is described. (2S,5S)-2,5-Dialkyl substituted piperazines 1 catalysed the enantioselective addition of dialkylzincs to aryl aldehydes. It was found that the presence of the dilithium salt of 1 was more effective in producing the corresponding alcohols in high e.e.s (up to 96% e.e.) and that the catalyst 1 with branched carbon chains as the substituents on the piperazine ring was effective for highly enantioselective reaction.