Enantioselective Synthesis of α‑Silylamines by Meerwein–Ponndorf–Verley-Type Reduction of α‑Silylimines by a Chiral Lithium Amide

Meerwein–Ponndorf–Verley-type
reduction of N-tosylsilylimines with chiral lithium
amide 2 affords α-silylamines in high enantioselectivity.
Since the
enantioselectivity observed was inconsistent with our previously proposed
chairlike six-membered transition structure, we performed density
functional theory (DFT) calculations on transition states leading
to (S)- and (R)-7a and
(S)- and (R)-7e using
an N-phenylsulfonyl derivatives 12 and 13 as model systems. Results of the calculations showed that
the structures are considerably deformed from the chairlike form with
steric repulsions between the 1′-methylene group and the imine-carbon
substituents playing an important role in the control of the enantioselectivity.