Multigram Synthesis\nof 3,3-Spiro-α-prolines

A series of novel spirocyclic α-proline building\nblocks with\na spiro conjunction in position 3 of the pyrrolidine ring was prepared\nto employ two convenient and practical synthetic approaches. Both\nalternative routes utilize simple and readily available starting materialscyclic\nketones and estersand comprise 6 and 7 steps, respectively.\nThe methodologies feature distinct advantages, using routine organic\nchemistry transformations, and are suitable for producing multigram\namounts of the target prolines. The approach also became valuable\nfor spirocyclic pyroglutamic acids.