The 1H NMR spectrum of compound 16 at room temperature only presents one set of resonances for the geminal protons of the pyrrolidine ring (δ ≈ 5.1 and 4.1), which implies a fast exchange between the two extreme cis and trans conformations for this nitrogen atom regarding the
organic addend.
Decreasing the temperature below 258 K induces the apparition of two sets of well-defined resonances at δ ≈ 5.1.

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