C(Cl)(=O)C(Cl)=O.CS(C)=O.[CH2:11]([C:18]1[C:23](=[O:24])[N:22]2[CH:25]=[CH:26][CH:27]=[CH:28][C:21]2=[N:20][C:19]=1[CH2:29][OH:30])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.C(N(CC)CC)C>ClCCl.C(OCC)(=O)C.O>[CH2:11]([C:18]1[C:23](=[O:24])[N:22]2[CH:25]=[CH:26][CH:27]=[CH:28][C:21]2=[N:20][C:19]=1[CH:29]=[O:30])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=126.5 mL (53.0 mmol) of oxalyl chloride in 40 mL dichloromethane was cooled to −78° C. To the resulting solution was added a solution of 7.52 mL (105.9 mmol) of DMSO in 24 mL dichloromethane and stirred at −78° C. for one hour. Then was added a solution of 4.7 g (17.65 mmol) of product from Step 5 (15) in 60 mL dichloromethane and the resulting mixture was stirred at −78° C. for one hour. Then was added 24.6 mL (176.5 mmol) of triethylamine and stirred at −78° C. for one hour. The mixture was then allowed to warm to 0° C. and stirred for another hour. Finally, the mixture was allowed to warm to ambient temperature over the course of one hour. Excess water was added to the reaction mixture and the mixture was extracted (3×) using dichloromethane. The combined organic layers were dried over MgSO4 and activated carbon and the solvent was removed in vacuo. The resulting material was subjected to flash chromatography on a 10 cm column. Elution with a gradient of 100% hexanes, 20% ethyl acetate in hexanes, 33% ethyl acetate in hexanes, 43% ethyl acetate in hexanes, and 50% ethyl acetate in hexanes yielded 3.1 g (11.7 mmol, 67%) of 3-benzyl-4-oxo-4H-pyrido[1,2-a]pyrimidine-2-carbaldehyde (16) as a yellow solid.
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