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

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Abstract
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.