Reagents Wittig

First the normal Wittig reaction, and then a second mol of Wittig reagent must be behaving as a carbene equivalent, just as we hoped the sulphur yhd would. 

This is a very challenging problem indeed. You may find some solutions by setting up two substituents on tlie carbon atom. For example, how about a substituted Wittig reagent ... 

In view of the synthetic importance of dicarbonvl compounds surprisingly little has been done, apart from carotene synthesis, on dialkenylation with Wittig reagents. However, from the few examples reported one may conclude, that no special problems are involved. Benzocyclobutanedione was converted by two equivalents of methoxycarbonylmethylidenetri-phenylphosphorane to the corresponding diene in 85% yield (M. P. Cava, 1960). 

The Wittig reaction uses phosphorus ylides (called Wittig reagents) to convert aldehydes and ketones to alkenes... 

A useful apphcation of phosphines for replacing a carbonyl function with a carbon—carbon double bond is the Wittig reaction (91). A tertiary phosphine, usually triphenylphosphine, treated with the appropriate alkyl halide which must include at least one a-hydrogen, yields the quaternary salt [1779A9-3] which is then dehydrohalogenated to form the Wittig reagent, methylenetriphenylphosphorane [19943-09-5] an yhde. 

The acylation of Wittig reagents provides the most convenient means for the preparation of allenes substituted with various electron-withdrawing substituents. The preparation of o-allenic esters has been accomplished by the reaction of resonance-stabilized phosphoranes with isolable ketenes and ketene itself and with acid chlorides in the presence of a second equivalent of the phosphorane. The disadvantages of the first method are the necessity of preparing the ketene and the fact that the highly reactive mono-substituted ketenes evidently cannot be used. The second method fails when the a-carbon... 

The aldehyde functionality present in 3-phenyl-2H-azirine-2-carbox-aldehyde reacts selectively with amines and with Qrignard and Wittig reagents to give a variety of substituted azirines. These azirines have been used, in turn, to prepare a wide assortment of heterocyclic rings such as oxazoles, imidazoles, pyrazoles, pyrroles, and benzazepins. ... 

Fluoroolefins may he prepared by the reaction of Wittig reagents and other pho sphorus-containtng y tides with fluorinated carbonyl compounds. (A discussion of the fluorinated Wittig reagents or other fluonnated phosphorus reagents with nonfluorinated carbonyl compounds is on page 581.) Tnphenylphosphoranes, derived from alkyltriphenyl phosphonium salts, react with 1,1,1-trifluoroacetone [3/] or other trifluoromethyl ketones [32, iJ] (equation 26) (Table 10). 

Burton [92J published extensive NMR information forjluorinatedquaternary phosphanium salts that are used as Wittig reagents Clear data-structure correlations allow NMR mformauon on other compounds to be predicted The trifluo-romethyl analogue is a recent addition to this senes [93] The fluonne NMR of... 

The sisyl ether is stable to Grignard and Wittig reagents, oxidation with Jones reagent, KF/18-crown-6, CsF, and strongly acidic conditions (TsOH, HCl) that cleave most other silyl groups. It is not stable to alkyllithiums or LiAlH4. 

The reaction of a cepham primary amine with 20 eq. of 37% formalin produces the dioxazine in 75% yield. The dioxazine is sufficiently stable to allow the formation of Wittig reagents and to carry out an olefination with formaldehyde. Treatment of the dioxazine with 6 N HCl in CH2CI2 releases the amine in excellent yield. ... 

Aldehydes can be prepared by the Wittig reaction using (methoxymethylene)-triphenylphosphorane as the Wittig reagent and then hydrolyzing the product with acid. For example,... 

Betaine (Section 19.11) A neutral dipolar molecule with nonadjacent positive and negative charges. For example, the adduct of a Wittig reagent with a carbonyl compound is a betaine. 

Wittig reagent for preparation of (9,0-d ichloro-/>-dim ethylamino-styrene, 46,33... 

Treatment of benzopentathiepin with Wittig reagents leads to 1,2,4-benzotrithiins, e.g. formation of 13.4U... 

Condensation of the dialdehyde 3 with the difunctional Wittig reagent 4 affords in low yield dibenz[[Pg.569]

The Wittig reagent 7 on reaction with the dialdehyde 8 gives a mixture of the isomeric highly substituted systems 9 and 10 in extremely low yields (0.7 and 1.4%, respectively).21... 

Wittig reagent, for preparation of 1,4-di-phenyl-1,3-butadiene, 40, 36 for preparation of methylenecyclo-hexene, 40,66... 

Allyltin compounds can be prepared by simple modifications of the usual reaction involving allyl Grignard reagents (139), by the 1,4-addition of trialkyltin hydrides to 1,3-dienes 140,141), or by the reaction of an aldehyde or ketone with the appropriate, tin-carrying, Wittig reagents (142). 

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