Acylation of (S)-(-)-4-amino-4-aryl-5,5,5-trifluoropentan-2-ones with chloroacetyl chloride gave the corresponding chloroacetamides which were treated with sodium azide and then with triphenylphosphine to obtain triphenyl-lambda(5)-phosphanylideneaminoacetic acid amides. The latter underwent thermal (boiling toluene) or base-catalyzed (NaOH/MeOH) intramolecular cyclization with elimination of triphenylphosphine oxide and formation of (7S)-(-)-7-aryl-5-methyl-7-trifluoromethyl-1,3,6,7-tetrahydro-2H-1,4-diazepin-2-ones.