Sodium triacetoxyborohydride → Ethyl 6-(2,3-di-p-tolyl-7,8-dihydropyrido[2,3-b]pyrazin-5(6H)-yl)hexanoate

A solution of 2,3-di-p-tolyl-5,6,7,8-tetrahydropyrido[2,3-b]pyrazine (Intermediate B) (2.0 g, 6.34 mmol) and ethyl 6-oxohexanoate (Intermediate A) (2.508 g, 12.68 mmol) in 1,2-dichloroethane (50 ml) was treated with sodium triacetoxyborohydride (3.36 g, 15.85 mmol) and the resultant suspension was stirred at room temperature overnight. The solution was treated with sat.NaHCO3 and extracted with DCM (×3). The organic extracts were dried (MgSO4) and evaporated under reduced pressure. The residue was loaded onto an Isolute® SCX-2 cartridge and eluted with MeOH followed by 2M NH3 in MeOH. The methanolic ammonia fractions were concentrated under reduced pressure and further purified by chromatography on silica eluting with 10-50% EtOAc in iso-hexane to afford the titled compound;