The Fluorenone Imines of Glycine Esters and Their Phosphonic Acid Analogues

Much more reactive than the corresponding benzophenone imines, which have often been used in the synthesis of α-amino acids, the title compounds undergo Mannich-type reactions with imines in the presence of a catalytic amount of a base to afford α,β-diamino acid and α,β-diaminophosphonic acid derivatives with high syn diastereoselectivity (see scheme). An asymmetric version of the reaction is also described. Boc=tert-butoxycarbonyl.