Efficient catalytic asymmetric prop-2-ynylation of achiral aldehydes with allenyltributylstannane promoted by a BINOL-Ti IV complex (10 mol%) is achieved with high enantioselectivity by the use of Et 2 BSPr i .
Catalytic enantioselective addition of (4-trimethylsilylbut-2-ynyl)tributylstannane to aldehydes provides trimethylsilylmethylallenyl alcohols in high enantioselectivity which can be converted with a second electrophile to the corresponding dienyl alcohols.
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1995 stereochemistry stereochemistry (general, optical resolution) O 0030
-023Asymmetric Cyclopropanation Using New Chiral Auxiliaries Derived from D-Fructose.-Acetals of α,β-unsaturated aldehydes with 3-Oalkylated derivatives of D-fructose-derived carbohydrates are cyclopropanated with CH2I2 and ZnEt2 with good diastereoselectivity. The effects of the acetal structure on the enantioselectivity are examined. Good enantioselectivity with high chemical yields is achieved especially with the endo acetals of the β-D-fructopyranose (e.g. (Va)). On the other hand, the isomers of psicopyranose give lower enantiomeric excesses than those of the fructopyranose derivatives. However, in both cases the enantiomeric excess of the exo acetal isomers is lower than that in the case of the endo forms. Cyclopropanation of cis enal acetals (e.g. (XIV)) leads to a mixture of products. -(KANG, J.; LIM, G. J.; YOON, S. K.; KIM, M. Y.; J.
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