PREPARATION, SEPARATION OF DIASTEREOISOMERS, AND X-RAY DETERMINATION OF CONFIGURATIONS OF ZOYLAMINO-5-[(1S)-METHYLPROPYL]-4-OXO-1,3-DIOXANES AND ZOYLAMINO-5-[(1S)-METHYLPROPYL]-4-OXO-1,3-DIOXANES

(5R)- and zoylamino-5-[(1S)-methylpropyl]-4-oxo-1,3-dioxanes were obta ined via alpha-hydroxymethylation of (4S)-2-phenyl-4-[(1S)-methylpropy l]-5 (4H)-oxazolone derived from N-benzoyl-L-isoleucine. The isomer 5R crystallized in a space group P2(1) with a = 7.071(1), b = 10.998(3), c = 9.884(1) Angstrom and beta = 109.58(2)degrees, while isomer 5S in a P2(1)2(1)2(1) with a 6.477(1), b = 10.023(1) and c = 21.901(6) Angs trom. The configurations of both diastereoisomers were established by X-ray methods. Semi-rigid conformation of the whole 5-benzoylamino-4-o xo-1,3-dioxane system is determined by flattening of the ring lactone fragment (resulting in O(1)-sofa conformation) and characteristic twis t (20 to 30 degrees) of the planar amide group in relation to the adja cent benzene ring.