Ammonium Chloride → tert-Butyl 6-cyano-4-hydroxy-spiro[chroman-2,4'-piperidine]-1'-carboxylate

To a solution of 15 g of tert-butyl 6-cyano-4-oxospiro[chroman-2,4′-piperidine]-1′-carboxylate in 250 mL of EtOH-THF(1:4) at 0° C. was added NaBH4 portionwise, and the reaction mixture was allowed to warm up to rt. After stirring for 1 h, NH4Cl aqueous was added to the reaction mixture and the aqueous mixture was extracted with AcOEt twice. The combined organic layers were washed with brine, dried over Na2SO4, filtered, and concentrated in reduced pressure to give the intended compound as a pale yellow solid.