Scheme 10. Synthesis of β-Lactones 35 and 36 from Known β-Lactone 4b.
Reagents and conditions: (a) N-Cbz-l-leucine, DIAD, PPh3, THF, 0 °C, 72%; (b) Pd/C (10% wt/wt), H2 (1 atm), THF, rt; DCC, formic acid, CH2Cl2, rt, 63%; (c) N-Cbz-d-leucine, DIAD, PPh3, THF, 0 °C, 82%; (d) Pd/C (10% wt/wt), H2 (1 atm), THF, rt; DCC, formic acid, CH2Cl2, rt, 60%.