1-Phenethylamine, (-)- → (S)-tert-butyl 4-(1-phenylethylimino)-3,4-dihydro-2H-spiro[naphthalene-1,4'-piperidine]-1'-carboxylate

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A solution of tert-butyl 4-oxo-3,4-dihydro-2H-spiro[naphthalene-1,4′-piperidine]-1′-carboxylate (A4) (5.0 g, 15.8 mmol), (S)-1-phenylethanamine (3.0 ml, 23.8 mmol) and boron trifluoride dimethyl etherate (0.5 ml, 5 mmol) in dry toluene (150 ml) was heated at 140° C. under a Dean-Stark trap for 24 hours. The solvent was distilled and the residue was cooled with an ice bath, dissolved in ethyl acetate, washed with saturated NaHCO3, and water. The organic phase was dried over Na2SO4, filtered and concentrated to give (S)-tert -butyl 4-(1-phenylethylimino)-3,4-dihydro-2H-spiro[naphthalene-1,4′-piperidine]-1′-carboxylate (B1) as a gum. LC-MS analysis of the crude indicated that there is trace of starting material (A4). LC-MS: m/e=419.37 (M+H). Rt=2.24 min.

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