**3. Terpenes**

*3.1. Monoterpenes*

3.1.1. Pantofuranoids

Pantofuranoids A–F (**29**–**34**) are monoterpenes that were isolated in 1996 from the Antarctic red alga *Pantoneura plocamioides* [30]. They are the first monoterpenes found to contain a tetrahydrofuran moiety, and their common framework (Figure 8) suggests that they all come from the same terpene precursor.

**Figure 8.** Proposed structure of pantofuranoids.

In 2006, Toste reported the enantioselective total synthesis of **(***−***)-33**, in which the key step is a vanadium-catalyzed sequential resolution/oxidative cyclization [31]. Using an in situ generated vanadium(V)–oxo complex with chiral tridentate Schiff base ligand **35** as catalyst, racemic homoallylic alcohol **36** was readily converted into 2,4-*cis*-substituted THF **37** (Scheme 3). The observed stereochemistry can be explained through a chair-like transition state in which coordination of the pseudo-equatorial ester group to the vanadium complex determines the selectivity of the *syn*-epoxidation step. Then, compound **37** was further elaborated to **(***−***)-33** in 6 steps and 29% overall yield from **37**.

**Scheme 3.** Vanadium-catalyzed synthesis of the tetrahydrofuranyl core of (−)-pantofuranoid E by Toste.
