The synthesis of amides and dipeptides from unprotected amino acids by a simultaneous protection–activation strategy using boron trifluoride diethyl etherate

The reaction of l-phenylalanine (1) with boron trifluoride diethyl etherate and primary amines leads to the formation of amides via a cyclic boron intermediate. It is also possible to use the amino dicarboxylic acid l-aspartic acid and N-alkylated amino acids (peptoid building blocks, e.g., NPhe-OH 9). The latter can be used in the preparation of dipeptidomimetics.