Other Alternative Methods. To a suspension of ethyl 6-amino-1-ethyl-4-oxo-1,8-naphthyridine-3-carboxylate in a solvent specified in Table 1 was added acetic acid and the mixture was stirred until all solids went into solution (may need to warm up to 40-45° C.). 2-Indanone was added to reaction mixture and stirred to completion of imine formation (indicated by disappearance of starting material in LCMS) (˜30 min to 1 h). Boron reducing agent (as listed in Table 1) was added to reaction mixture and stirred vigorously to completion of imine reduction (disappearance of imine in LCMS). The reaction mixture was transferred to a beaker, diluted with ethyl acetate, added an ice-cooled aqueous sodium hydroxide solution (1.0 M) (enough to quench almost 90% of acetic acid) and then further basified with solid sodium bicarbonate to pH 7-8. The organic layer was separated, washed with brine, dried over MgSO4 and evaporated under reduced pressure to dryness. Where specified in Table 1, the crude was passed through a plug of silica gel with increasing gradient of EtOAc in DCM to offer the required product as dark yellow solid.
