Preparation, separation of diastereoisomers, and X-ray determination of configurations of (5R)- and (5S)-5- benzoylamino-5-[(1S)-methylpropyl]-4-oxo-1,3-dioxanes

Abstract

(5R)- and (5S)-5-benzoylamino-5-[(1S)-methylpropyl]-4-oxo-1,3-dioxanes were obtained via a-hydroxymethylation of (4S)-2-phenyl-4-[(1S)-methylpropyl]-5(4H)-oxazolone derived from N-benzoyl-L-isoleucine. The isomer 5R crystallized in a space group P2₁ with a = 7.071(1), b = 10.998(3), c = 9.884(1) Å and β = 109.58(2)°, while isomer 5S in a P2₁2₁2₁ with a = 6.477{1), b = 10.023(1) and c = 21.901(6) Å. The configurations of both diastereoisomers were established by X-ray methods. Semi-rigid conformation of the whole 5-benzoylamino- 4-oxo-1,3-dioxane system is determined by flattening of the ring lactone fragment (resulting in 0(1)-sofa conformation) and characteristic twist (20 to 30) of the planar amide group in relation to the adjacent benzene ring.