Determination of the absolute configuration of (+)- and (−)-N-CBZ-3-fluoropyrrolidine-3-methanol using vibrational circular dichroism and confirmation of stereochemistry by conversion to (R)-tert-butyl 3-fluoro-3-(((R)-1-phenylethyl)carbamoyl)pyrrolidine-1-carboxylate

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Racemic N-CBZ-3-fluoropyrrolidine-3-methanol (±)-1 was resolved by preparative chiral HPLC. The absolute configuration of the enantiomers of 1 was identified by vibrational circular dichroism and confirmed by chemical synthesis, which involved exchanging the CBZ protecting group of (−)-1 with Boc, followed by oxidation with RuCl3, NaIO4, activation of the resulting acid with carbonyl diimidazole and reaction with (R)-α-methylbenzylamine to give (R)-tert-butyl 3-fluoro-3-(((R)-1-phenylethyl)carbamoyl) pyrrolidine-1-carboxylate 7. The latter was compared with authentic (S)-tert-butyl 3-fluoro-3-(((R)-1-phenylethyl)carbamoyl)pyrrolidine-1-carboxylate 6 and its diastereomer 7; the configuration of diastereomer 6 was obtained by an X-ray diffraction study. This established that the enantiomer (−)-1 had an (R)-configuration.