Studies toward the total synthesis of (+)-gelsemine and synthesis of spirocyclopentaneoxindole through intramolecular Michael cyclization

During the approach to the total synthesis of (+)-gelsemine, two novel spirocyclopentaneoxindole compounds 2 and 3 were obtained. Starting from compound 9, spirocyclopentaneoxindole 3 was efficiently and unexpectedly obtained through a Boc migration–intramolecular Michael cyclization cascade procedure. This intramolecular Michael addition strategy allows conveniently access to complex spirooxindole and spirocyclopentaneoxindole derivatives.