To a solution of 2,3-diphenyl-5,6,7,8-tetrahydropyrido[3,2-b]pyrazine (Ex. 4.1 step 1) (2 g, 6.96 mmol) in DCE (35 ml) was added pent-4-enal (2.061 ml, 20.88 mmol) and the mixture was stirred at RT overnight. A further portion of sodium triacetoxyborohydride (4.43 g, 20.88 mmol) was added and the mixture was stirred at RT for 2.5 hours under an atmosphere of nitrogen. Water was added and the mixture was extracted with EtOAc (3×60 ml). The combined organic extracts were dried over MgSO4, filtered and concentrated in vacuo. The crude material was purified by chromatography on silica eluting with EtOAc/iso-hexane to afford the title compound;
