276
S. S. Diwan, S. W. Dalvi, and H. R. Mulla
Pd=C (20 g of a 60% w=w aqueous suspension), and methanol (2 L) were
taken in a hydrogenation autoclave. The assembly was set up for heating,
and stirring was started. The reactor was filled with a hydrogen pressure
of 20 kg=cm2, and the temperature was set at 50 ꢁC. Gas chromatographic
analysis after 30 min showed complete disappearance of starting material.
The assembly was purged with nitrogen, and the catalyst was allowed to
settle. The supernatant was carefully decanted off, and the catalyst was
washed with methanol (2 ꢀ 500 mL). The washings were decanted off as
well. The catalyst was reused for subsequent batches of the same reaction.
The solvent was removed in vacuo, and the crude 4-dimethylaminopiper-
idine-1-carboxylic acid tert-butyl ester (3) was taken up in a 3-L, round-
bottom flask with an overhead stirrer. A solution of HCl in isopropanol
(1 L) was added to it with stirring, and the reaction was allowed to stir at
room temperature. A solid was slowly seen to separate out. TLC (chloro-
form–methanol, 9:1; Rf ¼ 0.05) after 2 h showed complete reaction. The
reaction was allowed to stir overnight at room temperature to aid preci-
pitation of the product. The stirring was stopped, and the solid residue
was filtered and washed repeatedly with isopropanol followed by ethyl
acetate. The solid was dried under a vacuum to get 184 g (91.5%) of
1
dimethyl-piperidin-4-yl-amine dihydrochloride (4) as a white solid. H
NMR (300 MHz, D2O) d ppm 1.85 (qd, 2H, J ¼ 13.5, 4.5 Hz), 2.27 (dt,
2H, J ¼ 13.5, 2.1 Hz), 2.80 (s, 6H), 3.01 (td, 2H, J ¼ 6.0, 1.5 Hz), 3.50
(m, 3H); 13C NMR (75 MHz, D2O) d ppm 23.3, 40.0, 42.6, 60.2; ESI
MS ¼ 129 (M þ 1þ); HPLC purity 100%.
ACKNOWLEDGMENTS
The authors thank Dr. F. Reutter and Dr. H. V. Joshi for helpful discus-
sions, Mrs. D. Kumbhar for help with the experiments, and Mr. Y. S.
Lakshminarasimham for analytical support.
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