[O:1]=[C:2]1[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][N:10]=2)N(C(OC(C)(C)C)=O)[CH2:4][CH2:3]1.[CH2:19]=[C:20]1[C:26]2=NC=CC=C2OCC[CH2:21]1.[C:31]([O-])(O)=[O:32].[Na+].CSC>CCOC(C)=O.O.C(Cl)(Cl)Cl.CO>[C:20]([C:9]1[N:10]=[C:11]2[C:2](=[O:1])[CH2:3][CH2:4][CH2:31][O:32][C:6]2=[CH:7][CH:8]=1)([CH3:26])([CH3:21])[CH3:19]tert-butyl 4-oxo-3,4-dihydro-1,5-naphthyridine-1(2H)-carboxylate. To a solution of 9-methylene-6,7,8,9-tetrahydrooxepino[3,2-b]pyridine (1 eq.) in a mixture of solvents (MeOH:CHCl3) is added a catalytic amount of NaHCO3. The reaction mixture is cooled to −78° C. and purged with O3. Reaction progress is monitored by TLC. After the reaction is judged complete, the reaction mixture is quenched with dimethyl sulfide (5 eq.) at −78° C. The resulting mixture is stirred for 12 h at ambient temperature. The reaction mixture is diluted with EtOAc and water. The organic layer is washed with water, dried over Na2SO4, and concentrated in vacuo. The compound that may be thus obtained is purified by column chromatography to give the title compound.
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