Total Synthesis of Mycolactones A and B.

First and second generation total syntheses of mycolactones A and B are reported. The first generation total synthesis unambiguously confirmed our earlier assignment of the relative and absolute stereochemistry of mycolactones A and B. Knowledge of the chemical properties of the mycolactones accumulated through the first generation total synthesis allowed us to implement several major improvements to the original synthesis, including: (1) optimizing the choice of protecting groups, (2) eliminating the unnecessary adjustment of protecting groups, and (3) improving the overall stereoselectivity and synthetic efficiency. The second generation total synthesis consists of 21 longest linear steps, with 8.8% overall yield.