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Polyphosphoric acid (25g) was heated at 100°C under nitrogen until it could be stirred. 1-(Toluene-4-sulfonyl)-1,2,3,4-tetrahydro-benzo[b]azepin-5-one (2.6g, 8.2 6mmol) was added portion-wise and the reaction mixture was heated at 100°C for 1.5h. It was poured into ice and basified with 2M NaOH(aq). The aqueous layer was extracted twice with dichloromethane. The organic extracts were combined, washed with brine, dried and reduced in vacuo. The residue was purified by flash chromatography on silica gel (eluant; 40percent EtOAc: 60percent hexane) to yield 1,2,3,4-Tetrahydro-benzo[b]azepin-5-one (1.05g, 79percent).

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