Diastereoselective Additions of (R)-(+)-Methyl p-Tolyl Sulfoxide Anion to Imines. Asymmetric Synthesis of (R)-(+)-Tetrahydropalmatine

Article abstract of DOI:10.1021/jo00293a045

The addition of the lithium carbanion of methyl phenyl sulfoxide and (R)-(+)-methyl p-tolyl sulfoxide to imines having at least one aryl substituent, under kinetically controlled conditions, gives β-amino sulfoxides with good to modest diastereoselection.Under equilibrium controlled condition poor product diastereoselection results.The addition of these anions to 3,4-dihydro-6,7-dimethoxyisoquinoline is unique in that the most favorable product diastereoselection (92:8) is observed under equilibrium controlled conditions.Deuteration experiments suggest that equilibration occurs via a β-amino α-lithio sulfinyl carbanion through a retro-Michael addition then Michael addition reaction sequence.This methodology allows for the construction of (R)-(+)-tetrahydropalmatine in four efficient synthetic steps.