Total synthesis of (-)-borrelidin.

The total synthesis of borrelidin has been achieved. The best feature of our synthetic route is SmI(2)-mediated intramolecular Reformatsky-type reaction for macrocyclization after esterification between two segments. The two key segments were synthesized through chelation-controlled carbotitanation, chelation-controlled hydrogenation, stereoselective Reformatsky reaction, and MgBr(2).Et(2)O-mediated chelation-controlled allylation. [reaction: see text]