A Convenient Synthetic Route to Spiro[indole‐3,4′‐piperidin]‐2‐ones

Starting from 1‐(tert‐butoxy)carbonyl]piperidine‐4‐carboxylic acid and 2‐bromoaniline, the spiroindole‐3,4′‐piperidin]‐2‐one system was obtained in three high‐yielding steps: anilide formation, N(1)‐protection, and intramolecular cyclization under Pd catalysis as the key reaction. The preparation of the corresponding 2‐bromoanilide was studied. In extension, the same sequence was developed with 4‐methyl‐ and 4‐nitro‐2‐bromoaniline. In the key step, the NO₂ group led to a rather diminished yield. The transformation of the protected spiroindole‐3,4′‐piperidin]‐2‐one to the corresponding unprotected dihydroindoles is discussed.