Full conversion in diastereoselective aldol additions using "naked" enolates under catalytic amount of phosphazene base: The hydroxypinanone as chiral auxiliary

It was shown that a 'naked' enolate can undergo an aldol addition with full conversion provided that the Delta pKa between the aldol product and the c onjugated acid of the base (which provides the necessary proton to the aldo l-adduct) is large enough (>6 units). Under such conditions the base being regenerated can be used in catalytic amounts. When the iminoglycinate is de rived from hydroxypinanone, 83% of the threo-isomer having similar to 98% e e (threonine) was obtained.