Stereoselective Synthesis of the C31-C41 Spirolactam Fragment of Sanglifehrin A

A stereoselective synthesis of the spirolactam fragment (C31–C41) of a highly‐potent immunosuppressant sanglifehrin A is described. The key steps involved in this synthesis are a desymmetrization protocol, Sharpless asymmetric epoxidation, Crimmins syn aldol reaction, Barton–McCombie deoxygenation, and acid‐mediated spirolactamization. An efficient and highly‐stereoselective synthesis for the spirolactam segment of the extremely potent immunosuppressant sanglifehrin A was successfully accomplished by following our own desymmetrization strategy, followed by Sharpless asymmetric epoxidation, Crimmins syn aldol reaction, Barton–McCombie deoxygenation, and spirolactamization as key reactions.