Dabco → Dimethyl 1,4,6,7-tetrahydropyrano[4,3-b]pyrrole-2,3-dicarboxylate

A suspension of dihydro-2H-pyran-4(3H)-one oxime (7 g, 60.8 mmol), dimethylacetylene dicarboxylate (9.72 ml, 79 mmol), and DABCO (2.046 g, 18.24 mmol) in Toluene (27.5 ml) were heated to 165° C. After 2 h, the reaction mixture was cooled to ambient temperature, concentrated in vacuo and purified by ISCO (0-100% EtOAc-hexanes) to afford dimethyl 1,4,6,7-tetrahydropyrano[4,3-b]pyrrole-2,3-dicarboxylate (3.2 g, 13.38 mmol, 22.00% yield) as a yellow solid. The residue was dissolved in DMF (30 mL), and treated with Cs2CO3 (5.29 g, 16.23 mmol) and 4-fluorobenzyl bromide (2.023 ml, 16.23 mmol). After 2 h, the reaction mixture was partitioned between EtOAc and sat. aq. NH4Cl. The organic layer was washed with water, brine, dried (MgSO4), filtered and concentrated in vacuo. The residue was purified by ISCO (0-50% EtOAc-hexanes; 120 g column) to afford dimethyl 1-(4-fluorobenzyl)-1,4,6,7-tetrahydropyrano[4,3-b]pyrrole-2,3-dicarboxylate (3.92 g, 11.29 mmol, 18.56% yield) as a yellow oil. LCMS (m/z) ES+=348 (M+1).