Understanding Internal Chirality Induction of Triarylsilyl Ethers Formed from Enantiopure Alcohols

Chirality transmission
from point chirality to helical chirality
was explored using triarylsilyl ethers. Circular dichroism (CD) spectroscopy
was employed to show that the alcohol stereocenter of silylated, enantiopure
secondary alcohols can transmit chirality to the aryl groups on the
silicon resulting in a higher population of one helical conformation
over another. Cotton effects characteristic of the aryl groups organized
into one preferred conformation were observed for all of the compounds
examined, which included both triphenyl- and trinaphthylsilyl groups.
Alcohols with an R configuration typically induced
a PMP helical twist, while an S configuration
induced a MPM helical twist. Molecular modeling combined
with solid-state structures also gave evidence signifying that point
chirality adjacent to triphenylsilyl groups could bias the conformation
of the phenyl groups. This work helps in our understanding of the
origin of selectivity in our silylation-based kinetic resolutions
and a role the phenyl groups play in that selectivity.