Asymmetric Synthesis of α-Substituted β-Amino Sulfones by aza-Michael Addition / α-Alkylation

Abstract

The aza-Michael addition of (S)-1-amino-2-methoxymethyl-pyrrolidine (SAMP) to alkenyl sulfones (E)-1, followed by reductive N-N bond cleavage with BH3×THF and N-benzylation yields N-benzyl-protected β-amino sulfones (R)-3 with high enantiomeric excesses (ee ≥ 96%). Subsequent α-alkylation of (R)-3 with various electrophiles leads to α-alkyl-β-amino sulfones (R,R)-4a-e in excellent yields (88-97%) and finally high diastereomeric (de = 96 - ≥ 98%) and enantiomeric purity (ee ≥ 96%). The absolute configuration was determined by X-ray structural analysis and confirmed by NMR spectroscopy (NOE-experiments).