Aniline → 3-(Phenylamino)butanoic acid

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A mixture of aniline (3.0 g, 32 mmol) and crotonic acid (2.0 g, 23 mmol) in toluene (20 mL) was heated at reflux for 18 h. Removal of solvent and chromatography (silica gel, EtOAc/hexane, 9/1) of the crude material afforded 2.5 g (61%) of 3-phenylaminobutanoic acid. The acid was treated with PPA (20 mL) at 110° C. for 6 h and the reaction mixture was poured into ice water (50 mL) and then was neutralized with Na2CO3 to pH 7. Extraction with EtOAc (3×60 mL) followed by chromatography (silica gel, EtOAc/hexane, 4/6) afforded 1.0 g (44%) of 1,2,3,4-tetrahydro-2-methyl-4-quinolinone (structure 59A of Scheme XLVIII, where R1 =R3 =H, R2 =methyl) as a yellow solid. The quinolinone was treated with di-tert-butyl dicarbonate (2.2 g, 10 mmol) and DMAP (0.84 g, 6.8 mmol) in THF (15 mL) for 16 h followed by chromatography (silica gel, EtOAc/hexane, 2/8) to afford 1.1 g (68%) of 1-tert-butoxycarbonyl-1,2,3,4-tetrahydro-2-methyl-4-quinolinone as a yellow oil. Data for 1-tert-butoxycarbonyl-1,2,3,4-tetrahydro-2-methyl-4-quinolinone: 1H NMR (400 MHz, CDCl3) 7.99 (d, J=7.5, 1 H), 7.78 (d, J=7.5, 1 H), 7.50 (t, J=7.5, 1 H), 7.12 (t, J=7.5, 1 H), 5.10 (m, 1 H), 3.04 (dd, J=17.3, 5.8, 1 H), 2.57 (dd, J=17.3, 1.7, 1 H), 1.56 (s, 9 H), 1.22 (d, J=6.9, 3 H).

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