The NHC-Catalyzed Enantio- and Diastereoselective [2 + 3] Annulation of Phthalide-Derived Alkenes with Enal Access to Bispiroheterocyclic Compounds Bearing Three Vicinal Stereogenic Centers

The N-heterocyclic carbene (NHC)-catalyzed enantio- and diastereoselective [2 + 3] annulation of alkenes derived from phthalide and isatin with α,β-unsaturated aldehydes resulting in the construction of bispiro-phthalide-cyclopentanone-oxindoles is demonstrated. The reaction proceeds via the generation of NHC-bond homoenolate intermediates from enals and NHC, which on interception with alkenes derived from phthalide and isatin afford bispiroheterocyclic compounds bearing three contiguous stereogenic centers in moderate to good yields with high enantio- and diastereoselectivities. The selective reduction of the carbonyl group facilitated the synthesis of bispiro-phthalide-cyclopentanol-indoline with a single diastereomer containing five stereocenters.