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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.

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 (1 S,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.

The use of chiral piperazines (cyclic diamines) 1 as chiral catalysts for the enantioselective addition of dialkylzincs t o aldehydes is described. (2S,5S) -2,5-Dialkyl substituted piperazines 1 catalysed the enantioselective addition of dialkylzincs t o 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 t o 96% e.e.) and that the catalyst 1 with branched carbon chains as the substituents o n the piperazine ring was effective for highly enantioselective reaction.

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