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The general procedure for the synthesis of 1-Boc-3-[(dimethylamino)methylene]-4-oxopiperidine from N-tert-butoxycarbonyl-4-piperidone and N,N-dimethylformamide dimethyl acetal was as follows: N,N-dimethylformamide dimethyl acetal (18 g, 20 mL, 151 mmol) was mixed with 1-(tert-butoxycarbonyl)piperidin-4-one (30 g, 151 mmol) were dissolved in N,N-dimethylformamide (240 mL) and the reaction was stirred at 80°C for 24 hours. After completion of the reaction, the reaction mixture was concentrated under reduced pressure to afford the target product 1-Boc-3-[(dimethylamino)methylene]-4-oxopiperidine as a yellow solid (38.4 g, 100% yield). Mass spectrum (ESI, positive ion mode) m/z: 255 [M + H]+.

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