反应详情

Preferably the 1,2,3,4-tetrahydro-2,7-naphthyridine intermediate (VIIb) can be synthesised as shown in Schemes 3 and 4. In Route B, commercially available 6-methoxynicotinaldehyde is treated successively with the lithium salt of N,N,N′-trimethylethylenediamine, then n-BuLi in hexanes and finally iodine to afford the 4-iodo-6-methoxynicotinaldehyde (cf. Tetrahedron Lett. 1993, 34(39), 6173-6176). The iodo compound is coupled with trimethylsilylacetylene under usual Sonagashira-Hagihara conditions (Synthesis 1980, 627-630) and the resulting 6-methoxy-4-[(trimethylsilyl)ethynyl]nicotinaldehyde is condensed with ammonium hydroxide in ethanol to give 3-methoxy-2,7-naphthyridine (Synthesis 1999, 2, 306-311). Regioselective catalytical reduction (cf. Eur. J. Med. Chem. Ther. 1996, 31(11), 875-888) affords 6-methoxy-1,2,3,4-tetrahydro-2,7-naphthyridine. Demethylation and N-protection with BOC-anhydride and finally treatment of the resulting tert-butyl 6-hydroxy-3,4-dihydro-2,7-naphthyridine-2(1H)-carboxylate with triflic anhydride in a two-phase system gives (VIIb).