Sodium Hydroxide → 1'-t-butoxycarbonylspiro[benzo[c]thiophene-1(3H),4'-piperidine]

Participants

Reaction Steps

81.0 g (0.40 mole) of 2-bromobenzylthiol were dissolved in 800 ml of tetrahydrofuran, and 516 ml of a solution containing 0.84 mole of butyllithium (as a 1.6 M solution in hexane) were added dropwise thereto over a period of 6 hours at a temperature of −78° C. The mixture was then stirred for 1.5 hours at the same temperature, after which 800 ml of a tetrahydrofuran solution containing 79.5 g (0.40 mole) of 1-t-butoxycarbonyl-4-piperidone was added dropwise thereto over a period of 3 hours. The solution was then stirred for a further 1 hour, and then a saturated aqueous solution of ammonium chloride was added, and the mixture was extracted with ethyl acetate. The organic extract was washed with a saturated aqueous solution of sodium chloride and then dried over anhydrous sodium sulfate. The solvent was then removed by distillation under reduced pressure. 2 liters of 4 N aqueous sulfuric acid were added to the residue, and then the mixture was heated under reflux for 14 hours. At the end of this time, the solution was made basic by the addition of 350 g (8.75 mole) of sodium hydroxide, whilst ice-cooling, and then 102 g (0.47 mole) of di-t-butyl dicarbonate were added thereto. The mixture was then stirred for 1 hour. At the end of this time, the product was extracted with methylene chloride, and the organic extract was washed with a saturated aqueous solution of sodium chloride and then dried over anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure, and the resulting residue was purified by silica gel column chromatography, using a 97:3 by volume mixture of hexane and ethyl acetate as the eluent, to give 56 g of the title compound as white crystals, melting at 131.0-132.5° C. (after crystallisation from hexane/ethyl acetate).

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