A Cascade Strategy Enables a Total Synthesis of (±)-Morphine

Morphine has been a target for synthetic chemists since Robinson proposed its correct structure in 1925, resulting in a large number of total syntheses of morphine alkaloids. Here we report a total synthesis of (+/-)-morphine that employs two key strategic cyclizations: 1) a diastereoselective light-mediated cyclization of an O-arylated butyrolactone to form a tricyclic cis-fused benzofuran and 2) a cascade ene-yne-ene ring closing metathesis to forge the tetracyclic morphine core. This approach enables a short and stereoselective synthesis of morphine in an overall yield of 6.6%.