Development of a Safe and Scalable Amine-to-Nitrone Oxidation:  A Key Step in the Synthesis of R107500

The stepwise optimization towards a safe, reproducible, and high-yielding oxidation of azepine 2 into the prochiral nitrone 4 is described, with emphasis on the elimination of Davis reagent 3. m-Chloroperoxybenzoic acid (mCPBA) was found to be an elegant and scalable alternative oxidant regarding safety, yield, and easy workup procedures. Nitrone 4 was obtained in 95% yield and used without purification or isolation in the cycloaddition step to provide oxazolidone 6 in high yield. The process was scaled up successfully to an 800-L scale (60 mol of starting material).