Example 1, Alternative Preparation, Step 2: Sulfonium salt 3 (619.4 g), and cesium carbonate (416.8 g) and anhydrous dimethyl sulfoxide (6.2 L) were combined in a reactor equipped with a scrubber to neutralize volatile sulfides. Vigorous agitation was maintained until complete conversion was obtained (HPLC). Ethyl acetate (12.4 L) was added, followed by 20% brine (3 L). The organic phase was separated, washed twice with brine (2×3 L) and evaporated to obtain a solution of ethyl (7R,8S)-8-((S)-3-benzyloxycarbonylamino-2-oxo-pyrrolidin-1-yl)-1,4-dioxa-spiro[4.5]decane-7-carboxylate 4 in ethyl acetate (˜0.8 L). Acetone (2.55 L) was added, followed by aqueous 0.5 M hydrochloric acid solution (2.3 L). With good mixing, the solution was heated to 50 to 60° C. until conversion of 4 to ethyl (1R,2S)-2-((S)-3-benzyloxycarbonylamino-2-oxo-pyrrolidin-1-yl)-5-oxo-cyclohexanecarboxylate 5 was complete (HPLC). The mixture was concentrated under reduced pressure while below 40° C., cooled to ˜30° C., and water (4.1 L) was added. The resulting slurry was cooled to 5 to 10° C. and agitated for ˜1 hour. The product was filtered and the cake was washed with water (2×2.5 L). Upon deliquoring, the cake was dried to a constant weight below 40° C. in a vacuum oven. Cyclohexanone 5 (272 g, 70% yield) was obtained (HPLC purity 98.7%).
