C(OC([N:11]1[C:20]2[C:15](=[CH:16][CH:17]=[CH:18][CH:19]=2)[CH2:14][CH:13]([C:21]([O:23][CH3:24])=[O:22])[CH2:12]1)=O)C1C=CC=CC=1.C([N-]C(C)C)(C)C.[Li+].Cl[C:34]([O:36][CH3:37])=[O:35].Cl>O1CCCC1.[Pd]>[CH3:37][O:36][C:34]([C:13]1([C:21]([O:23][CH3:24])=[O:22])[CH2:14][C:15]2[C:20](=[CH:19][CH:18]=[CH:17][CH:16]=2)[NH:11][CH2:12]1)=[O:35]
1.00 g of N-benzyloxycarbonyl-3(R,S)-methoxycarbonyl-1,2,3,4-tetrahydroquinoline (Example 1s)) are deprotonated in 10 ml of tetrahydrofuran with excess lithium diisopropylamide (1.5 equivalents) under customary reaction conditions, and 0.80 ml of methyl chloroformate is then added at -70° C. After 30 min, the mixture is poured onto 0.1N hydrochloric acid and extracted with methylene chloride. The crude product obtained after customary further working up is dissolved in 30 ml of tetrahydrofuran and hydrogenated in the presence of 1.00 g of palladium-on-charcoal (10% of Pd) until the reaction has ended. After purification of the product over 100 g of silica gel (mobile phase B), 3,3-bis(methoxycarbonyl)-1,2,3,4-tetrahydroquinoline is obtained: Rf (B)=0.50.
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