cis-(6RS,13RS)-3,3,10,10-Tetramethyl-6,13-diphenyl-1,8-dioxa-4,11-diazacyclotetradecane-2,5,9,12-tetraone and two of its precursors.

The title macrocycle, C26H30N2O6, (VI), was obtained by ;direct amide cyclization' from the linear precursor 3-hydroxy-N-[1-methyl-1-(N-methyl-N-phenylcarbamoyl)ethyl]-2-phenylpropanamide, the N-methylanilide of rac-2-methyl-2-[(3-hydroxy-2-phenylpropanoyl)amino]propanoic acid, C13H17NO4, (IV). The reaction proceeds via the intermediate rac-2-(2-hydroxy-1-phenylethyl)-4,4-dimethyl-1,3-oxazol-5(4H)-one, C13H15NO3, (V), which was synthesized independently and whose structure was also established. Unlike all previously described analogues, the title macrocycle has the cis-diphenyl configuration. The 14-membered ring has a distorted rectangular diamond-based [3434] configuration and intermolecular N-H...O hydrogen bonds link the molecules into a three-dimensional framework. The propanoic acid precursor forms a complex series of intermolecular hydrogen bonds, each of which involves pairwise association of molecules and which together result in the formation of extended two-dimensional sheets. The oxazole intermediate forms centrosymmetric hydrogen-bonded dimers in the solid state.