Optically pure N‐Boc‐norpandamarilactonine‐B was diastereoselectively synthesized starting from L‐serine by employing a double ring closing metathesis (RCM) of a tetraene derivative as a key reaction. N‐Boc‐norpandamarilactonine‐B obtained was further converted to pandamarilactonine‐A.