Dimethylformamide dimethyl acetal → tert-butyl 3-[(dimethylamino)methylene]-4-oxotetrahydro-1(2H)-pyridinecarboxylate

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A mixture of 1-tert-butoxycarbonylpiperidin-4-one and N,N-dimethylformamide dimethylacetal was heated under reflux with stirring for 6 hours to yield 1-tert-butoxycarbonyl-3-[(dimethylamino)methylene]piperidin-4-one. A mixture of 1-tert-butoxycarbonyl-3-[(dimethylamino)methylene]piperidin-4-one obtained, 2-hydrazinoethanol, and MeOH was heated under reflux with stirring for 2 hours to yield a mixture of 2-(5-tert-butoxycarbonyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-2-yl)ethanol and 2-(5-tert-butoxycarbonyl-4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridin-1-yl)ethanol. A mixture of the compounds obtained, 4M HCl-EtOAc solution, and EtOH was stirred at ambient temperature for 2 hours to yield a mixture of 2-(4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-2-yl)ethanol dihydrochloride and 2-(4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridin-1-yl)ethanol dihydrochloride.

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