Sulfuric Acid → 3-Methoxy-2,8-dimethyl-1-oxa-8-azaspiro[4.5]decane

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Reaction Conditions

Reaction Steps

A suspension of 1.05 g lithium aluminum hydride in 35 ml anhydrous tetrahydrofuran was cooled to 0° C., 0.92 ml of 100% sulfuric acid was added dropwise while maintaining the temperature in the range from 0° to 7° C., and the mixture was stirred for 30 minutes in the above temperature range. A tetrahydrofuran solution (7 ml) containing 711 mg 8-ethoxycarbonyl-3-methoxy-2-methyl-1-oxa-8-azaspiro[4,5]-decane was then added, and stirring was continued at that temperature for one hour. Ether (35 ml) was then added, sodium sulfate decahydrate (2.6 g) was further added in small portions, and stirring was continued for an additional one hour. The white suspension thus obtained was filtered using perlite as filter aid, and the filter cake was washed with a mixed solvent of ethanol/chloroform (1:5). The washings were joined to the filtrate, the combined solution was concentrated under reduced pressure, and the residue was dissolved in chloroform. This solution was dried over anhydrous magnesium sulfate, chloroform was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography using, as eluent, a mixed solvent of chloroform/methanol/conc. ammonia (10:1:0.1 by volume), giving 400 mg 3-methoxy-2,8-dimethyl-1-oxa-8-azaspiro[4,5]decane as oil. It was converted to hydrochloride by addition of ethanolic hydrogen chloride to its ethereal solution.

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