1-Benzoyl-4-benzylpiperidine-4-carboxylic acid → Spiro(1-indanon)-2,4'-(piperidine), N-benzoyl-

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A solution of 6.14 g (19.0 mmoles) 1-benzoyl-4-(phenylmethyl)-4-piperidinecarboxylic acid in 61 ml concentrated sulfuzic acid was stirred 18 hours at room temperature to give a deep red solution. The solution was carefully diluted with ice-bath cooling with 300 ml H2O and extracted with 3×300 ml ethyl acetate. The extract was washed with 25 ml water and brine, dried, and the solvent wam removed in vacuo to give a white foam. The foam was stirred under ether and filtered off to give 3.61 g (62%) product, m.p. 149°-154° C. 1H NMR (deuteriochloroform): δ1.50 (m, 2H), 2.00 (m, 2H), 3.12 (m, 2H), 3.25 (d of d of d, 2H), 3.90 (d, 1H), 4.62 (m, 1H), 7.43 (m, 7H), 7.63 (d of d, 1H), 7.79 (d, 1H).

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