Determination of the relative stereochemistry of 5α‐ and 5β‐diastereomers of [2α,3β,3aα]‐ethyl hexahydro‐2‐ (1,2,3,4‐ tetraacetoxybutyl)‐ 5,6,6‐ trimethylpyrrolo[1,2‐b] isoxazole‐3‐ carboxylate