First total synthesis of (+)-pentandranoic acid A

The first total synthesis of (+)-pentandranoic acid A (1) was accomplished in 14 steps, starting from alcohol 3. Our synthesis features several key transformations, such as an ozonolysis-aldol cyclization-dehydration ring contraction sequence and a selective 1,4-diol oxidation, and provides an efficient synthetic route to this rare clerodane diterpenoid.