Methyl iodide → (S)-di-tert-butyl 4,4-dimethyl-5-oxopyrrolidine-1,2-dicarboxylate

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Reaction Steps

To a solution of tert-butyl N-tert-butoxycarbonyl-4-methyl-L-pyroglutamate (1.2 g, 4.0 mmol) in tetrahydrofuran (20 mL) stirring at −78° C., was added a 1M solution of lithium hexamethyldisilazide in tetrahydrofuran (4.4 mL, 4.4 mmol) dropwise over 5 minutes. After 30 minutes, methyliodide (0.33 mL, 5.2 mmol) was added. After an additional 3 hours at −78° C., the cooling bath was removed and 50% saturated aqueous ammonium chloride (40 mL) was added. The solution was stirred for 20 minutes, then extracted with ether (2×50 mL). The combined organic layers were washed with water(2×25 mL), saturated sodium bicarbonate (2×25 mL), brine (50 mL), dried (Na2SO4), filtered and concentrated to give Boc-PyroGlu(4,4-dimethyl)-OtBu (0.673 g, 54%). Step 3. Synthesis of tert-butyl N-tert-butoxycarbonyl-4,4-dimethylproline (Boc-Pro(4,4-dimethyl)-OtBu)

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