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 /3-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 (8-amino a-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. © 1990, American Chemical Society. All rights reserved.