[sally]

In the next scheme is written in the article that they want to ensure the stereodivergence, so they invert the alcohols at C-9 and at C-12.
What is the meaning of stereodivergence and what is the purpose of this procedure?

[DavidW]

To achieve "stereodivergence" in a synthesis typically means that you are able to prepare all the stereoisomers, by making small modifications to the synthesis.  In this case, they do so by carrying out Mitsunobu reactions (first and second-to-last step) to invert the two stereocenters bearing the -OH groups.

[sally]

I still don't understand what's the purpose of stereodivergence?

[movies]

Sometimes the absolute and relative stereochemistry of a natural product isn't known, so you kind of have to guess.  The classic example of this is the synthesis of periplanone B by Still in 1979.  He prepared a bunch of different diastereomers of the natural product before he finally got it right.

There is a nice article on enantiodivergent synthesis here.

[DavidW]

Exactly.  Sometimes one only knows the "connectivity" of a natural product, but the stereochemistry may not be established.  By making all the possibilities, and then characterize all of them, one can single out the one with the correct relative/absolute stereochemistry by comparing the data..

Another useful application of stereodivergence would be in the case of biologically active compounds.  Sometimes it might be of interest to see how changes in the stereochemistry of the natural product can affect its biological activity.