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Proline derived [4.4]-spirolactams have been synthesised in good yields by a reductive-amination reaction followed by thermal cyclisation of the resulting amine onto the proline ester group in refluxing toluene. The synthesis of the corresponding [4.5]-spirolactams by the same method gave much reduced yields.
Kelleher, F., Kelly, S.: Spirobicyclic Diamines 1: Synthesis of Proline-derived Spirolactams via Thermal Intramolecular Ester Aminolysis. Tetrahedron Letters, vol.47 (18), 1 May 2006, p. 3005–3008.