Seiji Niwa

Kenso Soai; Seiji Niwa; Yasuyuki Yamada; Hideo Inoue

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.

Kenso Soai; Seiji Niwa; Hiroshi Hori

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.

Kenso Soai; Hiroshi Hori; Seiji Niwa

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

Seiji Niwa; Kenso Soai

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.

Kenso Soai; Yasuhiro Kawase; Seiji Niwa

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

Kenso Soai; Seiji Niwa; Takashi Yamanoi; Hitoshi Hikima; Miyuki Ishizaki

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.

Kenso Soai; Yuji Hirose; Seiji Niwa

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

Kenso Soai; Seiji Niwa; Toshihiro Hatanaka

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.

Kenso Soai; Seiji Niwa; Takashi Kobayashi

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.

Seiji Niwa; Kenso Soai

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.