**3. Conclusions**

Polyketides are a class of marine natural products with immense structural and biological diversity. They have interesting biological properties that sometimes make them potential drug candidates, such as in eribulin mesylate. Here, organic synthesis in general, and total synthesis in particular still play an important dual role. First, it is the final way of determining the correct structure of a product. Even though, nowadays, there are cuttingedge NMR techniques available, we still see many cases of structure misassignment in marine bioactive products. Secondly, the scarcity of some marine products makes them unavailable for research, and synthesis provides sufficient amounts for proper biological studies. The tetrahydrofuran motif is common among marine polyketides; thus, the development of new methodologies for the synthesis of tetrahydrofurans is a current need.

**Author Contributions:** Writing—original draft preparation, L.F.-P. and P.G.-A.; writing—review and editing, C.D.-P. and A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Junta de Castilla y León, gran<sup>t</sup> number VA294-P18.

**Acknowledgments:** C.D.-P. and L.F.-P. acknowledge predoctoral Grants funded by the European Social Fund and the "Junta de Castilla y León".

**Conflicts of Interest:** The authors declare no conflict of interest.
