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A mixture of anhydrous K2CO3 (3.2 g, 23.2 mmol, 5 eq) and 18-crown-6 (azetroped several times with toluene) (122 mg, 0.464 mmol, 10 mol %) in dry toluene (4 ml), under nitrogen, was heated to reflux and then treated, dropwise, over 40 min, with a solution of N-(4-Methoxy-benzyl)-N-(2-methoxycarbonyl-ethyl)-malonamic acid methyl ester. After 7 h at reflux the reaction was diluted with water (4 ml) and toluene (4 ml), then cooled to 0° and carefully acudified to pH 1.7 with 0.1N HCl. The mixture was then extracted several times with CH2Cl2 (3×80 ml) and the combined organics dried and evaporated to a brown oil (1.33 g). The brown oil was treated with 10% aqueous oxalic acid and heated to reflux for 6.5 h. The mixture was then extracted repratedly with CH2Cl2 and the combined organics dried and evaporated to a dirty yellow oil (1.03 g). The crude material was purified on silica gel using (CH2Cl2:MeOH=30:1) as eluent to give 1-(4-Methoxy-benzyl)-piperidine-2,4-dione as a pale brown solid (750 mg, 69%); (300 MHz, CDCl3) 2.52 (t, J=5.7 HZ, 2H), 3.41 (s, 2H), 3.47 (t, J=5.7 Hz, 2H), 3.80 (s,3H), 4.62 (s, 2H), 6.16-6.88 (m, 2H), 7.20 (m, 2H).

1. temperatureunder nitrogen, was heated
2. temperatureto reflux
3. additiontreated
4. temperatureAfter 7 h at reflux the reaction
5. temperaturecooled to 0°
6. extractionThe mixture was then extracted several times with CH2Cl2 (3×80 ml)
7. customthe combined organics dried
8. customevaporated to a brown oil (1.33 g)
9. additionThe brown oil was treated with 10% aqueous oxalic acid
10. temperatureheated
11. temperatureto reflux for 6.5 h
12. extractionThe mixture was then extracted repratedly with CH2Cl2
13. customthe combined organics dried
14. customevaporated to a dirty yellow oil (1.03 g)
15. customThe crude material was purified on silica gel using (CH2Cl2:MeOH=30:1) as eluent