Trifluoroacetic acid → (2-Ethylthiazol-4-yl)(1-oxa-4,9-diazaspiro[5.5]undecan-4-yl)methanone trifluoroacetate

Trifluoroacetic acid (20 mL) was added to a solution of tert-butyl 4-(2-ethylthiazole-4-carbonyl)-1-oxa-4,9-diazaspiro[5.5]undecane-9-carboxylate [Example 26, step a] (24 g) in dichloromethane (100 mL) and the mixture stirred at ambient temperature for 18 hours. The reaction mixture was diluted with toluene (50 mL) and concentrated in vacuo. The residue was dissolved in dichloromethane (50 mL), TFA (50 mL) was added and the mixture was stirred for 4 hours. The mixture was diluted with toluene (50 mL), concentrated in vacuo, the residue triturated with ether and the precipitated solid collected by filtration and dried to afford the subtitled compound as a white solid. Yield 28 g.