Methanol → 2-methyl-6,7-dihydroquinolin-8(5H)-one

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Reaction Steps

Intermediate 200A2 in dichloromethane (100 mL)/methanol (200 mL) was cooled to −78° C. Ozone was passed through the mixture for 1-2 h until the mixture had a light blue color. The reaction mixture was purged with nitrogen followed by the addition of dimethyl sulfide (10 mL). The mixture was stirred for 30 m and evaporated. The residue was partitioned between ether and 1M HCl. The organic layer was extracted with 1N HCl (2×) and the acidic, aqueous layers were pooled, washed with ether (3×), cooled with crushed ice, and carefully basified with solid NaOH. The basic layer was extracted with chloroform, freed of solvent, and the residue was passed through a column of SiO2 with 80% ethyl acetate/hexane to give impure Intermediate 200A3 as a yellow solid. Further purification of this mixture was conducted by oxidation of the minor product: (˜3%) 8-oxo-5,6,7,8-tetrahydro-quinoline-2-carbaldehyde in formic acid (15 mL) at 0° C. by dropwise addition of H2O2 (2.1 mL, 30% solution). The mixture was stirred for 1.5 h, quenched with crushed ice, diluted with chloroform, and basified with 2 M NaOH to pH>8. The chloroform layer was dried, filtered and evaporated to give pure 2-methyl-6,7-dihydro-5H-quinolin-8-one (Intermediate 200A3), 15.1 g (˜50% over two steps).

Provenance & Evidence