Stereocontrolled transformation of nitrohexofuranoses into cyclopentylamines via 2-oxabicyclo[2.2.1]heptanes. IV: Synthesis of enantiopure methyl (1S,2R,3R,4R,5S)-5-benzyloxycarbonylamino-2,3-isopropylidenedioxy-4-methoxycyclopentanecarboxylate