(2R,5S)-2-Trichloromethyl-3-oxa-1-azabicyclo[3.3.0]octan-4-one

Typical procedure: Introduction of an allyl group
To a flamedried 500-mL round-bottomed flask, diisopropylamine (10 mL, 71 mmol) is added to THF (140 mL) under argon. The reaction vessel is cooled to -78 °C before n-BuLi in hexane (1.6 M, 46 mL, 74 mmol) is added. The reaction mixture is stirred for an additional 30 min at -78 °C. In a separate 250-mL round-bottomed flask, T2902 (12.2 g, 49.9 mmol) is dissolved in THF (100 mL) and cooled to 0 °C with stirring for 10 min. A cannula is used to deliver the ethereal solution to the LDA solution at -78 °C under argon over 5 min. The resulting solution is stirred for an additional 20 min before the addition of allyl bromide (7.8 mL, 90 mmol). The reaction mixture is slowly allowed to warm to -40 °C, where it is maintained for an additional 2-3 h. The reaction mixture is then poured into a 1-L separatory funnel filled with 300 mL of water. The aqueous solution is extracted with chloroform (3x300 mL). The combined organic extracts are dried over Na₂SO₄ and concentrated in vacuo to afford the allyl lactone (10.7 g, 75%) as an orange oil.