Reaction Steps
2-Benzyl-4-trifluoromethanesulfonyloxy-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine-6-carboxylic acid tert-butyl ester. To a solution of 2-benzyl-4-hydroxy-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine-6-carboxylic acid tert-butyl ester (2.0 g, 5.9 mmol; prepared from 2-phenyl-acetamidine hydrochloride as described in Example 1, Step A) in THF (15 mL) was added KOtBu (0.408 g, 3.6 mmol). After 15 min, the mixture was treated with N-phenyl-bis(trifluoromethanesulfonimide) (1.18 g, 3.3 mmol) and the mixture was stirred for 18 h. The mixture was diluted with water and extracted with EtOAc (2×). The combined organic layers were dried and concentrated. The resulting residue was purified via SiO2 chromatography (10-40% EtOAc/hexanes) to give 1.15 g (81%) of the title compound which was contaminated with byproducts from N-phenyl-bis(trifluoromethanesulfonimide). Step B. 2-Benzyl-4-(4-fluoro-phenyl)-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine-6-carboxylic acid tert-butyl ester. The title compound was prepared as described in Example 1, Step C. MS (ESI): exact mass calcd. for C25H26FN3O2, 419.20; m/z found, 420.5 [M+H]+. 1H NMR (CDCl3): 7.53 (dd, J=5.3, 8.7, 2H), 7.43-7.41 (m, 2H), 7.31-7.28 (m, 2H), 7.23-7.14 (m, 3H), 4.55 (s, 2H), 4.27 (s, 2H), 3.75 (t, J=6.1, 2H), 3.00 (t, J=6.0, 2H), 1.43 (s, 9H). Step C. 2-Benzyl-4-(4-fluoro-phenyl)-5,6,7,8-tetrahydro-pyrido[4,3-d]pyrimidine. A solution of the product from Step B (0.131 g, 0.312 mmol) in CH2Cl2 was treated with TFA. After stirring for 4 h, the mixture was concentrated and partitioned between saturated (satd.) aq. NaHCO3 and CH2Cl2 (2×). The combined organic layers were dried and concentrated. The resulting residue was purified via SiO2 chromatography (1-7% 2 M NH3 in MeOH/CH2Cl2) to give 0.084 g (84%) of the title compound. MS (ESI): exact mass calcd. for C20H18FN3, 319.15; m/z found, 320.4 [M+H]+. 1H NMR (CDCl3): 7.51 (dd, J=5.4, 8.8, 2H), 7.41 (d, J=7.4, 2H), 7.31-7.27 (m, 2H), 7.22-7.19 (m, 1H), 7.15 (dd, J=8.7, 2H), 4.27 (s, 2H), 3.95 (s, 2H), 3.24 (t, J=6.1, 2H), 2.97 (t, J=6.1, 2H). Unless otherwise specified, the compounds in Examples 3-57 were prepared using methods similar to those described in Examples 1 and 2, utilizing the appropriate β-ketoesters, amidine hydrochlorides, and arylboronic acids.
