Ag(I)-Fesulphos-Catalyzed Enantioselective Synthesis of 3‑Silylproline Derivatives

An efficient catalytic asymmetric
1,3-dipolar cycloaddition of N-benzylidineiminoglycinate-derived
azomethine ylides to
β-silylmethylene malonates catalyzed by a Ag­(I)-Fesulphos complex
has been developed, affording fully substituted 3-silylproline derivatives
with an all carbon quaternary center. The silylproline derivatives
were obtained in moderate-to-good yields (up to 81%) in high diastereoselectivities
and enantioselectivities (dr up to 95:5; er up to 96:4). Tamao–Fleming
oxidation of selected 3-silylproline derivatives provided not only
an efficient route but also the shortest route to 3-hydroxyproline
derivatives, which are not accessible by direct 1,3-dipolar cycloadditions
of azomethine ylide with frequently used arylidene/alkylidene malonates.