Dimethylformamide → Tert-butyl 5-formyl-6-azaspiro[2.5]octane-6-carboxylate

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tert-butyl 6-azaspiro[2.5]octane-6-carboxylate (Intermediate 2, 1 g, 4.73 mmol) dissolved in 20 ml of Et2O was cooled to −60° C., then N,N,N′,N′-tetramethyl ethylendiamine (0.71 ml, 4.73 mmol) and secBuLi 1.4M in hexane (4.05 ml, 5.68 mmol) were added. After 10 minutes at −60° C., the temperature was raised to −20° C. for 30 minutes, then the reaction was cooled to −78° C. and dimethylformamide (0.55 ml, 7.09 mmol, dissolved in 5 ml of Et2O) was added. After 30 minutes a saturated aqueous solution of NH4Cl (8 ml) was slowly added, then reaction was allowed to reach room temperature. Reaction was extracted with Et2O (3×50 ml), the organic solvent was dried (Na2SO4) and evaporated to obtain a crude that was purified by silica gel chromatography (petroleum ether/ethylacetate from 95/5 to 85/15). (±) tert-butyl 5-formyl-6-azaspiro[2.5]octane-6-carboxylate was obtained as light yellow solid (400 mg).

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