Wittig-Homer-Emmons olefinations

Wittig-Homer-Emmons olefination of serinal derivative l-50 (see Scheme 13.27) with carbonylphosphorane 176 generates enone 177. Subsequent conversion to (—)-nojirimycin l-58 proceeds via anti dihydroxylation and reduction with NaBH4 (Scheme 13.61), whereas reduction with Red-Al leads to (—)-mannonojirimycin [109]. A similar approach has been applied to generate galactostatine [110]. 

The reaction has been extended to include carbanions generated from phosphonates. This is often referred to as the Horner-Wittig or Homer-Emmons reaction. The Horner-Emmons reaction has a number of advantages over the conventional Wittig reaction. It occurs with a wider variety of aldehydes and ketones under relatively mild conditions as a result of the higher nucleophilicity of the phosphonate carbanions. The separation of the olefinic product is easier due to the aqueous solubility of the phosphate by-product, and the phosphonates are readily available from the Arbusov reaction. Furthermore, although the reaction itself is not stereospecific, the majority favor the formation of the trans olefin and many produce the trans isomer as the sole product. 

The Witting reaction has been investigated in aqueous conditions.305 Wittig olefination reactions with stabilized ylides (known as the Wittig-Homer or Homer-Wadsworth-Emmons reaction) are sometimes performed in an organic/water biphase system.306 Very often, a phase-transfer catalyst is used. Recently, the use of water alone as solvent... 

The formation of allenes by Wittig or Homer-Wadsworth-Emmons-olefination of ketenes is well established [1] for more recent examples, see (a) T. Minami,... 

Several variants of the Wittig olefination reaction have been adapted to solid phase (Fig. 8). Williard et al. [43] prepared a series of stilbenes using the Homer-Emmons reaction on resin-bound aldehydes. A route to either substituted or unsubstituted unsatu-... 

Related reactions Horner-Wadsworth-Emmons olefination, Homer-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Takai-Utimoto olefination, Tebbe oiefination, Wittig reaction, Wittig reaction - Schiosser modification ... 

Hayashi, K.-L, Shinada, T., Sakaguchi, K., Horikawa, M., and Ohfune, Y., Olefination of dialkyl squarates by Wittig and Homer-Emmons reactions. A facile synthesis of 3,4-dioxo-l-cyclobutene-l-acetic acid esters. Tetrahedron Lett., 38, 7091, 1997. 

---