Toward asymmetric aldol-Tishchenko reactions with enolizable aldehydes: access to defined configured stereotriads, tetrads, and stereopentads.

Asymmetric aldol-Tishchenko reactions of enolizable aldehydes and ketones in the presence of chiral BINOLTi(OtBu)(2)/cinchona alkaloids complexes are described. Different configurative outcomes of these reactions depend on an equilibration through a retro aldol/aldol sequence and can be influenced by the configurative architecture of substrates. The results are explained by means of transition state models and rate constants.

Enantioselective direct aldol-Tishchenko reaction: access to chiral stereopentads.

[reaction: see text] The aldol-Tishchenko reaction of aromatic aldehydes in the presence of titanium(IV) tertbutoxide and amino alcohols is described. When used with cinchona alkaloids, stereopentads were isolated for the first time with a high degree of diastereo- and enantioselectivity.