Chiral titaniumcomplex (1), prepared in situ from optically pure binaphthol and diisopropoxytitanium dihalide in the presence of molecular sieves, is shown to catalyze the additionreactions of crotylsilanes and -stannanes to glyoxylates to afford (syn)-α-hydroxy-β-methyl esters in highly scalemic forms with high diastereoselectivity.
Enantioselective [2,3]Wittig rearrangement involving a chiral boron enolate terminus
作者:Katsuhiko Fujimoto、Takeshi Nakai
DOI:10.1016/s0040-4039(00)73309-0
日期:1994.7
The first enantioselective version of the ester enolate [2,3]Wittigrearrangement is described which involves a chiral boron enolate with a chiral bis-sulfonamide ligand to provide a high enantioselectivity(>95%ee), along with a high threo diastereoselectivity.
The title rearrangement of the chiral (E-crotyloxy)acetamides derived from (S)-prolinol has been shown to provide a modest level of asymmetricinduction (52–60%) along with a high erythro-selectivity (95–98%). The influence of the metal centers (Li, K, and Zr) and the ligating substituents on the prolinol part has been discussed.