Diisopropylethylamine → (R)-tert-butyl 4-(1-(4-chlorophenyl)ethylcarbamoyl)-4-cyanopiperidine-1-carboxylate

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O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (1.255 g, 3.30 mmol) was added in one portion to 1-(tert-butoxycarbonyl)-4-cyanopiperidine-4-carboxylic acid (Intermediate 43) (0.763 g, 3 mmol), (R)-1-(4-chlorophenyl)ethanamine (0.462 mL, 3.00 mmol) and DIPEA (1.572 mL, 9.00 mmol) in DMA (20 mL) at 25° C. under nitrogen. The resulting solution was stirred at 60° C. for 4 hours. The reaction mixture was evaporated to dryness and redissolved in DCM (150 mL), and washed sequentially with 1M aqueous citric acid (50 mL), water (50 mL), and saturated sodium hydrogen carbonate (100 mL). The organic layer was dried over magnesium sulfate, filtered and evaporated to afford crude product. The crude product thus obtained was concentrated, then purified by flash silica chromatography, elution gradient 0 to 100% EtOAc in isohexane. Pure fractions were evaporated to afford (R)-tert-butyl 4-(1-(4-chlorophenyl)ethylcarbamoyl)-4-cyanopiperidine-1-carboxylate (1.100 g, 94%) as a colourless gum which solidified on drying under high vacuum. This material was then redissolved in DCM (20.00 mL), and trifluoroacetic acid (2.311 mL, 30.00 mmol) was added. The solution was stirred at room temperature for 3 hours, after which the crude product was purified by ion exchange chromatography, using an SCX column. The desired product was eluted from the column using 7N ammonia/MeOH and pure fractions were evaporated to dryness to afford (R)—N-(1-(4-chlorophenyl)ethyl)-4-cyanopiperidine-4-carboxamide (0.720 g, 82%) as a colourless gum. This material was used directly in the next step without further purification.

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