NEt3 (2.0 ml) and TBTU (2.56 g) are added to a solution of 2-(1,4-dioxaspiro[4.5]decan-8-yl)acetic acid (1.45 g; see J. Med. Chem. 1998, 41(5), 760) in DMF (50 ml) and the mixture is stirred for 30 min. 2 M Dimethylamine in THF (7.24 ml) is added. The reaction mixture is stirred for one hour and the solvent is removed under reduced pressure. The residue is dissolved in EtOAc and washed with water and aqueous citric acid (10%, 2×). The organic layer is dried (Na2SO4) and filtered, and the solvent is removed under reduced pressure. The crude product is purified using reverse phase HPLC (Varian C18 Microsorb) eluting with a gradient of 10-100% acetonitrile in water containing 0.2% trifluoroacetic acid to give N,N-dimethyl-2-(1,4-dioxaspiro[4.5]decan-8-yl)acetamide (400 mg) and N,N-dimethyl-2-(4-oxocyclohexyl)acetamide (420 mg).
