Development of A Chiral Homoenolate Equivalent which Reacts Selectively with Imines

点击翻译按钮获取中文摘要

A chiral allyltitanium compound, prepared in situ by the reaction of optically active acrolein 1,2-dicyclohexylethylene acetal with a divalent titanium reagent, Ti(O-i-Pr)_4/2i-PrMgCl, reacts with a variety of acyclic and cyclic imines in a regiospecific way to afford cc-addition products as a mixture of the E- and Z-isomers in good combined yield, where the former is predominant in a ratio of 92:8 to >95:5. The mixture of (E)- and (Z)-adducts and pure (E)-adducts which could be isolated in several cases were respectively converted to the corresponding β-amino esters to confirm the absolute configuration and enantiomeric purity. The ee of the newly-formed asymmetric center is more than 78 % for the mixture of (E)- and (Z)-addition products and more than 96 % for pure (E)-isomer. By taking advantage of the versatility of the vinyl ether moiety in reaction products, optically active γ-amino aldehydes, γ-amino aldehyde acetals, y-amino acids, β-amino esters, andpyrrolidinoisoquinolines were readily prepared. In the reaction of the allyltitanium with optically active cc-silyloxyimine, remarkable double stereodifferentiation was observed; thus, the reaction of the allyltitanium derived from (S,S)- or (R,R)-1,2-dicyclohexylethylene acetal provided syn- and anti-adducts in a ratio of 55 : 45 or 0 : 100 respectively. Meanwhile, the stereochemistry of the product in the reaction with β-silyloxyimine was controlled mainly by the allyltitanium. The reaction could be effectively applied to prepare 4-amino-6-hydroxypentadecanal dimethyl acetal, a key intermediate for the synthesis of batzelladine D.