Wittig reaction of ylides

Miscellaneous Reactions.- The Schlosser-Wittig reaction of ylide (209) with aldehyde (208) and treatment of the intermediate 6-oxido ylide with perchloryl fluoride has been used to construct the 13-fluoro unit (210) in a total synthesis of (+)-13-fluoroprosta-... 

A study comparing, under a range of conditions, diene synthesis by the two alternative Wittig routes, allylic ylide-saturated aldehyde (route 1) and reactive ylide-a,P-unsaturated aldehyde (route 2), has been reported. 9 por the system chosen (Scheme 2) the reactive ylide-a,P-unsaturated aldehyde route is clearly preferred in that the stereochemistry of the new double bond can be controlled more easily and there is little or no isomerisation of the double bond already present in the aldehyde. A route to symmetrically substituted polyenes containing an odd or even number of double bonds has been reported (Scheme 3).20 The Wittig reactions of ylides derived from... 

Carotenoids, Retenoids, Pheromones and Polyenes. - (Ali- )-(3iS, 5R,6R)-Paracentrone (199), first isolated from the sea urchin Paracentrotus lividus, has been synthesised using Wittig reactions of ylides (197) and (198) as key steps. The Wittig reaction continues to be used in the synthesis of retinals, for example, side-chain methyl-shifted analogues, but little or no new chemistry has been reported. ( )-Selective Wadsworth-Emmons olefination using the a-sulfonylalkylphosphonate (200) followed by stereospecific desulfonylation has been used to synthesise the sex pheromone (201) of the potato tuberworm moth Phthorimaea operculella. ... 

Wittig reactions of the ylides (126) and (127) have been used in the synthesis of dimethyleicosatrienoic acids. The eicosatetraenoic acids (130) and (131), which are metabolites of LTB4, have been synthesized using Wittig reactions of ylides (128) and (129), respectively. Arachidonic acid metabolites (132) and (133) have been prepared by c/j-olefination with ylides (134) and (135). ... 

A recently reported asymmetric synthesis of the macrocyclic lactam macebecin uses selective (Z)-olefination with the fluoroethyl phosphonate ester (190) to introduce the (E,Z)-dienic amide residue. A Wittig reaction of ylides (191) with biphenyl aldehydes (192) has been used to link rings C and D in new convergent synthesis of the macrocyclic bis(biphenyls), plagiochin C and D. ... 

The intramolecular approach of Staab and Graf, shown in Scheme 4, precluded formation of 5, but was considerably more involved [12]. The cyclic dienyne 6 was afforded by Wittig reaction of o-phthaldialdehyde with the corresponding bis(ylide) derived from tolane. Bromination of 6 and subsequent treat-... 

The first synthesis of derivatives (77) of pentatetraene-carboxylic acid has been reported using a Wittig reaction of 1-H-allene-l,3-dicarboxylate monoester chlorides (76) in the presence of triethylamine.60 In one case an intermediate was obtained and was converted to (77) by further treatment with base. The reaction of carbon suboxide with phosphonium ylides has also... 

Wittig reactions of the thermally unstable ylide (231), generated in situ by the reaction of 2.2-dichlorohexafluoropropane with triphenylphosphine, have been used to prepare novel... 

Some difficult Wittig reactions of stable phosphorus ylides with ketones have been accelerated by microwave irradiation (Scheme 6.17) [63]. When compared to conventional method, an improved yield has been achieved within a shorter time using MW irradiation in the absence of solvent. 

Intramolecular Wittig reaction of keto-stabilized ylide 28 took place in refluxing toluene leading to the 1H-dihydropyrrolizines 31 in the case of a-ketocarboxylic derivatives <2001T5873>, while trifluoroacetyl ylide 28c afforded exclusively the 3//-dihydropyrrolizine 30c (Scheme 26) <2006ARK55>. 

Heterocycles.—The phosphonium salt (59) is an effective three-carbon synthon, as demonstrated by its reaction with enolates of /9-keto-esters (Scheme 20) to give cyclopentenyl sulphides via an intramolecular Wittig reaction.63 Ylides are also intermediates in the synthesis of dihydrofurans (60) from the cyclopropylphos-phonium salt (61) and sodium carboxylates (Scheme 21).64 Cumulated ylides are very useful for the synthesis of heterocyclic compounds, e.g. (62), from molecules which contain both an acidic Y—H bond and a carbonyl or nitroso-function, as shown in Scheme 22.65... 

Alternatively, bromo trienyne 66, prepared by the Wittig reaction of TMS-capped propargyl ylide with , -5-bromo-2,4-pentadienal, could be coupled with dienyl zinc reagent 67, as illustrated in equation 3657. Subsequent desilylation followed by treatment with trimethyl aluminum in the presence of catalytic Cp2ZrCl2 afforded the alane of tetraenyne 68 which, on exposure to chloroformate, gave essentially all- polyene ester 69. 

The results of ab initio (HF and MP2) and MNDO-PM3 molecular modelling of the Wittig reaction of unstabilized (Me3P=CHMe), semistabilized (Me3P=CHC=CH) and stabilized (Me3P=CH-CN) ylides with ethanal have been compared with experimental findings. ... 

It has been suggested that the preferential formation of ( )-alkene on Wittig reaction of amide-substituted phenyl 3-pyridyl ketones with non-stabilized phosphorus ylides which contain a carboxyl terminus is a consequence of either hydrogen bonding or salt... 

The normal Wittig reaction of nonstabilized ylides with aldehydes gives Z-olefms. The Schlosser modification of the Wittig reaction of nonstabilized ylides furnishes f-olefins instead. 

After these results had established the feasibility of generating and utilizing a carbohydrate phosphorane, the two systems that had been reported earlier were examined in order to determine if similar conditions would allow them to undergo the Wittig reaction. The ylide derived from phosphonium salt I condensed with both benz-aldehyde and U-chlorobenzaldehyde to produce good yields of olefinic products Villa and Vlllb. The ylide derived from phosphonium salt II also was successfully condensed with benzaldehyde, but the yield of IX was only 30 , presumably because of its extremely poor solubility even in an HMPA-THF solvent mixture. Both of these systems supported the tenet that it was possible to use unstabilized carbohydrate phosphoranes if the conditions are proper and if the g-oxygen is attached to the carbohydrate through another set of bonds. 

Wittig olefination of 5(4//)-oxazolones with triphenylphosphonium methylides affords product mixmres that depend on the ylide and the starting oxazolone. ° The product mixtures can include, apart from the expected 5(4//)-oxazolylideneace-tates, 5-oxazoleacetates, and other byproducts. Nevertheless, Wittig reaction of ethyl (triphenylphosphoranylidene)acetate with a 4,4-disubstituted-5(4//)-oxazo-lone 285 affords the corresponding ethyl 5(4//)-oxazolylideneacetates 286 in satisfactory yields (Scheme 7.93 Table 7.24, Fig. 7.26). 

The unsaturated ylide 48 has been prepared and shown to undergo Wittig reactions <71TL4873> and the Wittig reaction of both it and its tributyl analogue 49 has been used in synthesis of a natural product analogue <74AJC1491>. 

The preparation of norbomadiene-fused thiophene (17) involved a double-Wittig reaction of 1,2-dione 15 with the bis-ylide derived from phosphonium salt 16 <99BCSJ1597>. The effect of the fused heteroaromatic ring of 17 (neighboring group participation) on electrophilic substitution of the norbomadiene ring was examined. 

Furans having a double bond at position 2 can be obtained by a phosphine-initiated cyclization of enyne ketones in the presence of an aldehyde. The reaction may involve the 1,6-addition of the phosphine toward the enyne, ring closure and Wittig reaction of the ylide with the aldehyde <99TL3753>. 

E. Vedjs, T. Fleck and S. Hara, Evidence against reversible Wittig reaction of stabilised ylide high... 

Frattini, S., Quai, M. and Cereda, E., Kinetic study of microwave-assisted Wittig reaction of stabilised ylides with aromatic aldehydes, Tetrahedron Lett., 2001, 42(39), 6827-6829. 

The hemiacetal exists as an equilibrium mixture of cyclic compound 20 and its open counterpart (21), but an aldehyde addition reaction can occur only with the acyclic form A Wittig reaction of the stabilized ylide leads to an a. (3-unsaluraied ester that has the configuration with respect to the double bond. This reaction occurs under neutral conditions, so 1,4-addition of the alcohol to the a.p-unsaturated ester is avoided.6 A subsequent DIBAH reduction leads to ally lie alcohol 6 in a reaction that ordinarily shows complete 1,2-selectivit. ... 

The salt-free Wittig reaction of non-, semi-, and stabilized ylides has been investigated on realistic systems using density functional theory (DFT) calculations, including... 

This variation of the Wittig reaction uses ylides prepared from phosphonates.12 The Horner-Wadsworth-Emmons method has several advantages over the use of phosphoranes. These ylides are more reactive than the corresponding phosphoranes, especially when substituted with an electron withdrawing group. In addition the phosphorus product is a phosphate ester and soluble in water - unlike the Ph3PO product of the Wittig reaction - which makes it easy to separate from the olefin product. Phosphonates are also cheaper than phosphonium salts and can easily be prepared by the Arbuzov reaction from phosphanes and halides. 

The synthesis of poly-dibenzylidene-l,3-dithietane 201 is based on the Wittig reaction of/ -xylcnc-bis(triphcnyl-phosphonium) chloride 199 with carbon disulfide <2001MM346, 2002MM3806>. The phosphonium salt 199 was converted to the ylide 200, which reacted with carbon disulfide, yielding, after methanolysis, a thioketene. The latter was stirred at room temperature for 12 h to provide the polymeric compound 201, bearing 1,3-dithietane moieties in 54% yield (Scheme 25) <2001MM346, 2002MM3806>. 

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