**9. Other transformations**

A wealth of further transformations have been found to be possible in combination with Wittig/HWE reactions. Thus, cyclopropanation of alkenes using sulfur-ylide reagent **166** can be run in tandem with a Wittig reaction with a conjugated phosphorane such as **21**. This combination of reactions can be performed with the preparation of the aldehyde as the Wittig substrate by oxidation of the corresponding alcohol **165** with MnO2 in one pot (**Scheme 42**) [177].

**Scheme 42.** One-pot oxidation—Wittig-olefination—cyclopropanation.

Generally, non-stabilized phosphoranes are basic. This basicity has been used by Knüppel et al. in the transformation of α,α-dibromoenone **168** with excess methylenetriphenylphosphorane, where the phosphorane induces a Corey-Fuchs-reaction-type dehydrobromination/debromination to generate a terminal alkyne, which together with the concomitantly run Wittig-olefination delivers **169**, an intermediate to the trisnorsesquiterpene (−)-clavukerin A (**171**) (**Scheme 43**)

**Scheme 43.** Wittig-olefination—Corey-Fuchs-reaction-type dehydrobromination/debromination.

[178]. A metathesis reaction completes the sequence to **171**. In this case, the metathesis reaction is not run in one pot with the previous transformations.

Nevertheless, one-pot Wittig—metathesis reactions are well known from the literature [179–181]. A typical example is shown in **Scheme 44**, where catalyst **174** serves both as a catalyst for the metathesis as well as for the Wittig olefination, when the *in situ* produced aldehyde **175** is treated with triphenylphosphine and ethyl diazoacetate (**176**) in one pot (**Scheme 44**).

**Scheme 44.** One-pot Wittig—Metathesis reaction.
