p-Toluenesulfonic acid → 6-Fluoro-3,3-dimethyl-3,4-dihydro-1H-quinoxalin-2-one

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Reaction Steps

A mixture of N-(5-fluoro-2-nitrophenyl)-2-methylalanine methyl ester (XI, EXAMPLE 7, 11.2 g), palladium on carbon (10%, 0.63 g), and methanol (350 ml) is shaken under 44 psi of hydrogen pressure for 1.5 hr. Additional palladium on carbon (10%, 0.23 g) is added and the mixture is shaken at 36 psi for another 45 min. p-Toluenesulfonic acid (0.46 g) is added and the catalyst is filtered off. The filtrate is concentrated to about 150 ml and warmed at 800 for 75 min. The solvent is then removed under reduced pressure and the residue is chromatographed on silica gel (700 ml) eluting with dichloromethane/methanol (98/2). aaa a solid. The product is crystallized from methanol/dichloromethane/hexane to give the title compound, mp 148.5°-149.0°; NMR (CDCl3) 1.42, 3.80, 6.40, 6.46, 6.66 and 8.35 δ.

Provenance & Evidence