Abetmet: A wide variety ~&aminoe&ers are prepa& in good yields by the reaction c$ lithium ester enolates derived from ketene silyl acetals with N-(alkylamino)benzotriazoles.
The seco&uy fl-aminoesters readily qyclize to &tactuma @azetidinones) on depn3tonation. &Aminoacids and their derivatives are an important class of compounds; for example, they are precursors to the 3-lactam moiety found in antibiotics. 1 Since the interest in 3-lactams continues unabated,2 refined methods for their preparation, and those of the 3-aminoester precursors, are still of considerable value. Several methods are known for their preparation of simple fl-aminoacids, such as palanine, usually involving hydrolysis of a suitable precursor. Examples include the Amdt-Eistert homologation reaction of N-protected a-aminoacids and the Michael addition of nitrogen nucleophiles to a&unsaturated acids, esters or nitriles. s A recent report from our group on the synthesis of j3-amino esters involves the Reformatsky reaction of a-bromoesters on N-Mialkylamino)benzotriazoles giving various tertiary j3-aminoesters in good yields. 4 Other known procedures involve the treatment of N-(1methoxyalkyl)carbamates with lithium enolates yielding &(metboxycarbonylamino)propanoates,s tbe hydrolysis of dihydroxyuracils in alkaline mediume to give &amino acids, and the reduction of oximes, or N-acetyl oximes, of &ketc estera7 Recently, Ojima et. al. found that ketene silyl acetale add to Schiff bases in the presence of titanium