Homer-Wittig olefination

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

Interestingly, a phosphine oxide was used as a reagent in a Wittig-Homer olefination aiming at the synthesis of the key intermediate of vitamin D3... 

Synthetic analogues have been prepared as exemplified in Scheme 14 [95]. A first Wittig-Homer olefination of aldehyde 107, followed by acidic treatment, generates cyclohexenone 108. Chemo- and stereoselective reduction of the latter with 9-BBN followed by sy -selective epoxidation of the allylic alcohol (lateral hydroxyl group control) by w-chloroperbenzoic acid gives 109. Selective tosylation of its secondary alcohol moiety (steric hindrance makes the tosylation of the tertiary alcoholic moiety difficult) and subsequent deprotonation of the tertiary alcohol with NaH provide an alcoholate that undergoes an intramolecular displacement reaction. 

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... 

Asymmetric Wittig-Homer reaction chiral olefinations. 2 Reaction of the chiral ketone 1 with the ylide from (- )-8-phenylmenthyl phosphonoacetate (2) at -30 to -60° gives the (E)-olefin in a 90 10 ratio. The geometry of the alkene is determined mainly by the chiral auxiliary. Use of ent-2 results in 3 with the E/Z... 

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]. 

Aldehyde functions have been used as such to synthesize Schiff bases °, various stilbene derivatives by Wittig-Homer-type olefination or cinnamic acids or by Knoevenagel condensation with malonic acid . They can also be reduced to or oxidized to As examples for derivatives obtained via alcohol functions,... 

Petrova, J., Coutrot, P, Dreux, M.. and Savignac. P. The a-chlorination and carbonyl olefination. Arylchloromethanephosphonic acid esters. Preparation, alkylation, and Wittig-Homer reactions. Synthesis, 658, 1975. 

Tyvorskii, V.I., Tishchenko, I.G., Nakhar. P, and Benitsevich, M.S., PO-olefination (Wittig-Homer reaction) of formyloxiranes. Synthesis and transformation of 4,5-epoxy-2-pentenoic acid derivatives, Zh. Org. Khim., 18, 540, 1982 7. Org. Chem. USSR (Engl. Transl.). 18, 472, 1982. 

In contrast to the Wittig—Homer method, which provides almost exclusively -olefins, Wittig reaction of a suitably stabilized ylid in methanol as solvent with the in situ aluminate obtained from DIBAL reduction of 4 provides, after purification and separation of the dia-stereomers, a 55% yield of 30 with the Z,Z-configuration. Subsequent cyclopropanation and oxidative workup leads to aldehyde 32, which has been used to prepare the biologically active insecticide ( S)-deltamethrin (33) [20] (Scheme 8). 

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