Scheme 2. Synthesis of 2-(methylthio)-6-phenylpyrido[2,3-d]pyrimidin-7-one intermediates A9d-t.

* Reagents and conditions: (a) KF/Al2O3, DMA, rt, 3-4 h (23-60%); (b) R2I, NaH, DMF, 50 °C, 1 h (28-74%); (c) TBSCl, DMAP, imidazole, DMF, 0 °C to rt, overnight (88%); (d) MeI, K2CO3, acetone, reflux, 8 h (95%).