Spirobicyclic diamines 1: synthesis of proline-derived spirolactams via thermal intramolecular ester aminolysis

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.