**4. Wittig- and HWE reactions and C**─**C-coupling reactions in one-pot procedures**

Wittig- and Horner-Wadsworth-Emmons reactions can be combined with C─C-coupling reactions such as Suzuki cross-coupling [111–113], Mizoroki-Heck reaction [113–118] and Sonogashira-reaction [119]. Initially, it was observed that conjugated phosphoranes were stable under reaction conditions used for Heck- or Suzuki reactions (**Scheme 9**). Thus, phosphoranes themselves could be functionalized by Suzuki- [120], Mizoroki-Heck- [121], or Sonogashira-type [119] cross-coupling reactions, either in solution or when polymer-bound [122]. These phosphoranes could then be subjected to normal Wittig-olefination reactions with ketones or aldehydes [120–122]. The one-pot Wittig-Heck-reaction strategy can be extended to include an *O*-alkylation, where the Wittig reaction of a *p*-hydroxybenzaldehyde (**43**) with methylenetriphenylphosphorane, obtained *in situ* from phosphonium salt **44** provides the *p*-hydroxystyrene as the olefin component in the Mizoroki-Heck reaction in the presence of an alkyl bromide (e.g., **45**), which *O*-alkylates the phenoxy-function to give alkoxystilbenes **46** (**Scheme 9**) [123].

various aldehydes in one pot that lead after a further dehydrogenative step to substituted

Tandem-, Domino- and One-Pot Reactions Involving Wittig- and Horner-Wadsworth-Emmons...

http://dx.doi.org/10.5772/intechopen.70364

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Interesting is the cycloaddition of *in situ* produced benzyne (**55**) to 1,4-diphenylbutadiene, prepared *in situ* by HWE reaction from cinnamaldehyde, (**15**) give 1,4-diphenylnaphthalene

The transformation sequence Diels-Alder/Wittig can be part of a more complex reaction chain. Thus, Ramachary and Barbas III [135] have forwarded a Domino Wittig/Knoevenagel/

stilbenes and styrenes (**Scheme 11**) [133].

**Scheme 10.** Oxidation—Wittig-olefination—Diels-Alder reaction sequence.

**Scheme 11.** Cobalt (I)-catalyzed Diels Alder reaction—Wittig reaction.

**Scheme 12.** One-pot HWE reaction**—**cycloaddition of *in situ* produced benzyne.

(**56**) (**Scheme 12**) [134].

**Scheme 9.** One-pot Heck cross-coupling/Wittig reaction.
