To a stirring suspension of 3.5 g (0.021 mole) of 1-methyl-4-amino-1-azaspiro[4.5]decane of Example 2 and 150 ml of 10% NaOH was added dropwise 3.1 g (0.022 mole) of benzoyl chloride. The reaction was stirred vigorously for 24 hours, the aqueous solution was decanted and the remaining oil was dissolved in ethyl acetate and dried over Na2SO4. The solvent was then evaporated to give a solid which was recrystallized from hexane to give 2.5 g. The solid was dissolved in 10 ml of acetonitrile and 1.1 g of fumaric acid was added. The suspension was stirred until the amine salt precipitated from solution. The compound was filtered and recrystallized twice from ethanol-ether to give 2.1 g (25.7%) of 1-methyl-4-benzamido-1-azaspiro[4.5]decane fumarate, m.p. 171°-173° C.
