Efficient synthesis of (S)-4-phthalimido-1,3,4,5-tetrahydro-8-(2,6-dichlorobenzyloxy)-3-oxo-2H-2-benzazepin-2-acetic acid (Pht-Hba(2,6-Cl-2-Bn)-Gly-OH)

4-Amino-2-benzazepin-3-ones have proven very useful for studying the biolog ically active conformations of peptides. The synthesis of Pht-Aba-Xaa-OH by reaction of the corresponding 1,3-oxazolidin-5-one with trifluoromethanesu lfonic acid (TFMSA) has been reported in the literature. However, when this procedure was applied to the preparation of Pht-Hba(Bn)-Gly-OH 8, many byp roducts were formed and the yield of the desired aminobenzazepinones 7 and 8 was very low. We report in this paper an efficient methodology for the sy nthesis of Pht-Hba(2,6-Cl-2-Bn)-Gly-OH 17 starting from the commercially av ailable tyro sine. In our procedure, the dipeptide Pht-Tyr(2,6-Cl-2-Bn)-Gly -OH 15 is converted,to the 1,3-oxazolidin-5-one 16 Which then undergoes Fri edel-Crafts cyclization in the presence of tin tetrachloride to afford the desired 4-phthalimido-1,3,4,5-tetrahydro-8-(2,6-dichlorobenzyloxy)-2-benzaz epin-3-one 17 in excellent yield.