The silylation of 4-acetoxy-2-pyrrolidone (I) with trimethylchlorosilane (II) by means of triethyl amine in THF gives the corresponding N-trimethylsilyl derivative (III), which is condensed with 4-methoxybenzoyl chloride (IV) by means of NaHCO3 in THF yielding 1-(4-methoxybenzoyl)pyrrolin-2-one (V). Finally, this compound is reduced with H2 over Pd/C in ethyl acetate.
The condensation of 4-aminobutyric acid (VI) with acid chloride (IV) by means of NaOH in water gives 4-(4-methoxybenzoylamino)butyric acid (VII), which is then cyclized by means of P2O5 in phosphoric acid.
The condensation of 6-methoxy-2-naphthaldehyde (I) with acetone by means of NaOH in water gives 4-(6-methoxy-2-naphtyl)-3-buten-2-one (II), which is reduced with H2 over Pd/C in ethyl acetate.
The condensation of 6-methoxy-2-naphthaldehyde (I) with ethyl aceto-acetate (II) gives ethyl 2-(6-methoxy-2-naphthylmethylene)acetoacetate (III), which is reduced to ethyl 2-(6-methoxy-2-naphthylmethyl)acetoacetate (IV). Finally, this compound is hydrolyzed and decarboxylated in acidic medium.
By condensation of 2-bromo-6-methoxynaphthalene (I) with 3-buten-2-ol (VI) catalyzed by Pd(OAc)2 or PdCl2, along with PPh3 and NaHCO3 in 1-methyl-2-pyrrolidone at 140 C. The reaction of 2-bromo-6-methoxynaphthalene (I) with Mg in THF gives the expected Grignard reagent (VII), which is then condensed with 3-buten-2-one (II) by means of ZnCl2-amine complex in the same solvent.
The condensation of 2-bromo-6-methoxynaphthalene (I) with 3-buten-2-one (II) by means of PdCl2, PPh3 and K2CO3 in DMF at 132 C gives 4-(6-methoxy-2-naphthyl)-3-buten-2-one (III), which is then hydrogenated with H2 over Pd/C in DMF. The same condensation can be performed with PdCl2 , PPh3 and NaHCO3 in 1-methyl-2-pyrrolidone at 130 C. The reaction of 4-hydroxy-2-butanone (IV) with acetic anhydride or acetyl chloride gives 4-acetyl-2-butanone (V), which is condensed with 2-bromo-6-methoxynaphthalene (I) by means of PdCl2, PPh3 and K2CO3 in DMF at 132 C to yield the previously reported 4-(6-methoxy-2-naphthyl)-3-buten-2-one (III).
The reduction of methyl 6-methoxy-2-naphtyl acetate (III) with LiAlH4 in refluxing ether gives 2-(6-methoxy-2-naphthyl)ethanol (IV), which by treatment with PBr3 in refluxing benzene is converted into 2-(6-methoxy-2-naphthyl)ethyl bromide (V). The reaction of (V) with KCN in refluxing ethanol - water affords 3-(6-methoxy-2-naphthyl)propionitrile (VI), which is finally treated with methylmagnesium iodide in refluxing ethanol.
A short, simple and economical process for large-scale preparation of nabumetone has been reported: Condensation of commercially available 2-acetyl-6-methoxynaphthalene (2-acetylnaroline) (I) with ethyl acetate (II) by means of potassium sec-butoxide (sec-BuOK) in DMSO gives the ketoenol (III), which is reduced with H2 over Pd/C in ethyl acetate with a catalytic amount of sulfuric acid.
The bromination of beta-naphthol (I) gives the 1,6-dibromo-beta-naphthol (II), which is partially debrominated with Sn and BrH, yielding 1-bromo-beta-naphthol (III). The methylation of (III) with methanol/sulfuric acid affords the corresponding methyl ether (IV), which is treated with Mg and DMF to provide 6-methoxynaphthalene-2-carbaldehyde (V). The condensation of (V) with ethyl acetoacetate (VI) gives the expected adduct (VII), which is reduced with H2 over Pd/C to provide 2-acetyl-3-(6-methoxy-2-naphthyl)propionic acid ethyl ester (VIII). Finally, this compound is decarboxylated with aqueous HCl.