Asymmetric substitution at silicon

CHED 351

Emily Blamer, blamere@student.gvsu.edu and William R. Winchester, winchesr@gvsu.edu. Department of Chemistry, Grand Valley State University, 1 Campus Drive, Allendale, MI 49401
It is common to generate a carbon stereocenter by addition reactions to sp2 hybridized carbon, such as alkenes or carbonyl groups. For silicon, because the routes to silenes or disilenes are fewer, this has proven to be a less attractive route to stereogenic silicon centers. The reaction of a nucleophile with a prochiral silane of the type R1R2SiL2 generates a chiral at silicon silane. We are investigating the influence of R1. R2 and L on the enantioselective substitution reaction at silicon with organolithium nucleophiles using the chelating diamine Sparteine.

We will present the results of our studies comparing methoxy vs hydride as a leaving group and showing that use of methoxy as a leaving group led to higher enantioselectivity. We have also observed that increasing the difference in bulkiness of R1 and R2 leads to an increase in the enantioselectivity of the reaction. We will also be presenting our efforts at analyzing these reactions using chiral HPLC as well as polarimetry.