Reaction Steps
1,5-Naphthyridines of formula (53), wherein R4 and R5 are as defined in formula (I) and R6 is aryl or heteroaryl, can be prepared as described in Scheme 7. 3,7-Dibromo-[1,5]naphthyridine, prepared as described by W. W. Paudler, J. Org. Chem., 33:1384 (1968), can be treated with (2-ethoxyvinyl)tributylstannane, a halide source, such as, but not limited to, tetraethylammonium chloride, and a palladium source, such as, but not limited to, dichlorobis(triphenylphosphine)palladium (II) in a solvent, such as, but not limited to, N,N-dimethylformamide with heat (about 50° C. to about 150° C.) to provide 3-bromo-7-[2-ethoxyvinyl]-1,5-naphthyridine. 3-Bromo-7-[2-ethoxyvinyl]-1,5-naphthyridine can be treated with an acid, such as, but not limited to, formic acid at about 0° C. to about 60° C. in a solvent, such as, but not limited to, 1,2-dichloroethane to provide (7-bromo-1,5-naphthyridin-3-yl)acetaldehyde. Alternatively, 3-bromo-7-[2-ethoxyvinyl]-1,5-naphthyridine in a solvent, such as, but not limited to, tetrahydrofuran can be treated with an aqueous acid, such as, but not limited to, hydrochloric acid at about 0° C. to about 60° C. to provide (7-bromo-1,5-naphthyridin-3-yl)acetaldehyde. (7-Bromo-1,5-naphthyridin-3-yl)acetaldehyde can be treated with an amine of formula (5) under reductive amination conditions, such as, but not limited to, sodium triacetoxyborohydride and an acid, such as, but not limited to, acetic acid in a solvent, such as, but not limited to, 1,2-dichloroethane at about 0° C. to about 50° C. to provide amines of formula (52). Amines of formula (52) can be treated with boronic acids of formula (7), a palladium source, such as, but not limited to, tris(dibenzylideneacetone)dipalladium (0), a ligand, such as, but not limited to, tri(tert-butyl)phosphine, and a base, such as, but not limited to, potassium fluoride in a solvent, such as, but not limited to, tetrahydrofuran at about 20° C. to about 80° C. to provide 1,5-naphthyridines of formula (53).
