Amino acids intermolecular condensation reaction

Despite these mechanistic and theoretical studies, intermolecular amine-catalyzed aldolizations have only rarely been used on a preparative scale. A few note vorthy exceptions in vhich aldehydes are used as donors are sho vn in Scheme 4.6 [51-55]. These reactions are often performed neat or in the presence of small amounts of an organic solvent. The catalyst usually used is either a primary or secondary amine, a combination of an amine vith a carboxylic acid, or simply an amino acid. These catalyst systems have previously been used in the Knoevenagel condensation and it is apparent that synthetic amine-catalyzed aldolizations originate from Knoevenagel s chemistry [56]. 

Replacement of the aliphatic acid residue in the 1-amino-l-deoxy-L-arabinitol derivatives by an aromatic dicarboxylic acid gave the precursor 80. Attempted polymerization of 80 afforded, instead of the expected poly(ester amide), a mixture of oligomers (81) and the monomeric 1-deoxy-l-phthalimido-L-arabinitol derivative 82. When the reaction was conducted in hexamethylphosphoric triamide, these products were obtained in 30 and 51% yields, respectively, indicating that intramolecular condensation competes with the intermolecular reaction,59 This case illustrates a limitation of the active ester " method of polymerization (Scheme 19). 

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