Asymmetric synthesis of alpha-amino 1,3-dithioketals from sulfinimines (N-sulfinyl imines). Synthesis of (2S,3R)-(-)-3-hydroxy-3-methylproline.

[reaction: see text] N-Sulfinyl alpha-amino 1,3-dithioketals are prepared in high de and good yield by treating sulfinimines with lithio-1,3-dithianes. Selective removal of the N-sulfinyl or the thioketal groups affords stable alpha-amino 1,3-dithioketals and N-sulfinyl alpha-amino ketones, respectively. This new sulfinimine-derived chiral building block is employed in the asymmetric synthesis of polyoxypeptin amino acid (2S,3R)-(-)-3-hydroxy-3-methylproline.