[CH3:1][O:2][C:3]([N:5]1[CH2:10][CH2:9][CH:8]([C:11]([O:13][CH2:14][CH3:15])=O)[C:7](=[O:16])[CH2:6]1)=[O:4].[CH2:17]([OH:20])[CH2:18][OH:19].C1(C)C=CC(S(O)(=O)=O)=CC=1.C1C=CC=CC=1>C(OCC)(=O)C.C(Cl)Cl.O>[CH2:17]1[O:20][C:11]([CH:8]2[CH2:9][CH2:10][N:5]([C:3]([O:2][CH3:1])=[O:4])[CH2:6][C:7]2=[O:16])([O:13][CH2:14][CH3:15])[O:19][CH2:18]1
A mixture of ethyl 1-methoxycarbonyl-3-oxopiperidine-4-carboxylate (9.0 g; 39 mmol), ethylene glycol (100 ml), 4-toluenesulfonic acid (0.7 g), and benzene (500 ml) was refluxed for 6 days using a Dean-Stark water separator. The mixture was washed with aqueous sodium carbonate (300 ml; 1 M), water (300 ml), and saturated aqueous sodium chloride (300 ml). The organic phase was dried (K2CO3) and evaporated in vacuo to give 8.6 of an oil. CC [silica gel (Woelm 0.063-0.1 mm): 350 g; eluents: methylene chloride to which ethyl acetate (20-35%) was added] followed by ball-tube distillation at 40 Pa (oven temperature 170° C.) gave VIIIa (7.0 g; 65%) as a colourless oil. IR (film): 2970 (s), 2900 (s), 1730 (s) cm-1. 1H NMR (CCl4): δ4.05 (q, J 7 Hz) and 3.92 (s) (a total of 6H), 3.60 (s) and 3.7-3.0 (m) (a total of 7H), 2.8-2.5 (1H, t), 2.2-1.6 (2H, m), 1.23 (3H, t, J 7 Hz).
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