General procedure for the synthesis of tert-butyl 6-bromo-4-oxospiro[benzodihydropyran-2,4-piperidine]-1-carboxylate from 1-(4-bromo-2-hydroxyphenyl)ethanone and N-tert-butyloxycarbonyl-4-piperidone: In a 500 mL three-necked flask equipped with a reflux condenser, a CaCl2 drying tube, and a magnetic stirrer, 0.1 mol N-tert-butoxycarbonyl-4-piperidone (19.5 g) and 0.116 mol pyrrolidine (8.95 g) were dissolved in 100 mL of anhydrous methanol. Subsequently, 0.0837 mol 1-(4-bromo-2-hydroxyphenyl)ethanone (18 g) was added at room temperature. The reaction mixture was refluxed with stirring at 60-65 °C for about 3 hours. After completion of the reaction, the mixture was transferred to a rotary evaporation flask and the methanol was removed by distillation to give an orange viscous liquid. To the residue 75 mL of water was added and the product was extracted four times with 100 mL of ethyl acetate. The aqueous layer was separated and discarded and the organic layer was dried with anhydrous Na2SO4. After filtration, ethyl acetate was removed by distillation to give an orange viscous oil, which was further dried thoroughly under vacuum. Purification by column chromatography (eluent: ethyl acetate/petroleum ether, 10/90, v/v) afforded 28.7 g (87% yield) of a light yellow crystalline solid. The melting point of the product was 140-143 °C.
