Determination of the absolute configuration of the diterpene tonantzitlolone B

In this work synthetic and semi-synthetic studies toward the antitumor active natural product tonantzitlolone B are described, starting with an advanced intermediate obtained from the total synthesis of tonantzitlolone and a natural sample of this compound, respectively. The unknown absolute configuration of the stereogenic center in the side chain was elucidated to be (R).