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

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A mixture of 1-tert-butoxycarbonyl piperidine-4-one and N,N-dimethylformamide dimethylacetal was stirred for 6 hours heated to reflux to give 1-tert-butoxycarbonyl-3-[(dimethylamino)methylene]piperidine-4-one. A mixture of the obtained 1-tert-butoxycarbonyl-3-[(dimethylamino)methylene]piperidine-4-one, 2-hydrazinoethanol and MeOH was stirred for two hours heated to reflux to give a mixture of 2-(5-tert-butoxycarbonyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridine-2-yl)ethanol and 2-(5-tert-butoxycarbonyl-4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridine-1-yl)ethanol. A mixture of the obtained mixture, 4M HCl-EtOAc solution and EtOH was stirred for two hours at room temperature to give a mixture of 2-(4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridine-2-yl)ethanol dihydrochloride and 2-(4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridine-1-yl)ethanol dihydrochloride.

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