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In a flask fitted with a Dean-Stark trap and reflux condenser, a solution of 3-nitro-propionaldehyde (138 g, 1.34 mol) in toluene (1 L) was treated with ethylene glycol (83 g, 1.34 mol) and p-toluenesulfonic acid monohydrate (5.0 g, 26 mmol). The mixture was heated at reflux, open to air, for 4 h, and then cooled to rt. A black residue was removed by paper filtration. The filtrate was washed with satd. aq. NaHCO3 (250 mL) and brine (3×100 mL). Charcoal and MgSO4 were added, and the resulting suspension was stirred for 1 h. Filtration and concentration of the filtrate gave the title compound, which was used in the next step without further purification. 1H NMR (400 MHz, CDCl3): 5.03 (t, J=3.6, 1H), 4.50 (t, J=6.8, 2H), 4.05-3.90 (m, 2H), 3.90-3.80 (m, 2H), 2.44 (td, J=6.8, 3.6, 2H).

1. customIn a flask fitted with a Dean-Stark trap
2. temperaturereflux condenser
3. temperatureThe mixture was heated
4. temperatureat reflux, open to air, for 4 h
5. customA black residue was removed by paper filtration
6. washThe filtrate was washed with satd
7. additionCharcoal and MgSO4 were added
8. filtrationFiltration and concentration of the filtrate