Wittig reagents phosphorus

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

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). 

The migration of a C=C bond to form a C=N bond was also observed with hydro-xylamine [78, 79], hydrazine [80, 81] and primary amines [82]. The /f iminylphos-phine oxide formed in the reaction may serve as a Wittig reagent in the presence of a base to react with a ketone or an aldehyde leading to ,/fun saturated alkenyl-imines 153 (Scheme 10.74). The phosphorus group can be a phosphonium salt as well as a phosphonate. 

Alkenes are obtained from selective hydrogenation of alkynes (see Section 5.3.1), and the reaction of a phosphorus ylide (Wittig reagent) with an aldehyde or a ketone (see Section 5.3.2). 

If the coupling is to another element (here phosphorus) then the coupling appears once in each spectrum. The Wittig reagent has an A3P CH3-P) system proton A appears as a doublet, while the phosphorus atom appears as a quartet in the phosphorus spectrum at a completely different frequency. 

These reactions are also useful syntheses of vinyl phosphine oxides and of vinyl silanes. The stabilization of anions is weak—weaker than from phosphorus or sulfur—but still useful. The Wittig reagent used to make allyl silanes earlier in this chapter illustrates this point. 

Terminal phosphinidene-metal complexes, L TM=PR, readily add to double bonds (equation 17). Both metal-stabilized and phosphine-stabilized phosphinidenes, R P= PR3, can act as phospha-Wittig reagents, which undergo metathesis reactions with carbonyl-containing compounds to generate carbon phosphorus double bonds (equations 18 and 19). Pnictinidenes and their complexes have been extensively reviewed in terms of both their syntheses and reactivities. ... 

Alkyl halides, as well as sulfonates, besides being useful for the preparation of derivatives as shown above, are widely utilized for the preparation of phosphorus derivatives such as R-PPhi Hal , precursors for the generation of Wittig reagents. Alkyl halides are also extremely important as intermediates in the preparation of the most valuable derivatives of oxidation level 0, the organometallic compounds. The required reduction step is usually carried out via direct reaction of the alkyl halides with an active metal such as lithium or magnesium. 

The phosphorus ylide may be obtained from a wide range of different halides, and thus ketones may be converted into a range of unsaturated compounds. A useful reaction with the methoxymethylene Wittig reagent leads, via the acid-labile enol ether, to an aldehyde (Scheme 3.48). 

The phosphorus ylide 109 (Wittig reagent) was treated with a variety of aldehydes to provide a selection of 2-ylidene-l,3-diselones 110 along with a significant amount of the dihydro compound 111 (Equation 11) <1996JOC2877>. Compound 103 was obtained in this manner from terephthaldehyde <1998T13257>. 

There is striking difference in the mode of reaction of sulfur ylides and phosphorus ylides (Wittig reagent) with aldehydes and ketones. The former ylides lead to epoxides, whereas the Wittig reagent furnishes alkenes, pointing to the low affinity of sulfur toward oxygen compared to that of phosphorus. 

Shah, S., Protasiewicz, J. D. "Phospha-variations" on the themes of Staudinger and Wittig phosphorus analogs of Wittig reagents. Coord. Chem. Rev. 2000, 210, 181-201. 

In Section 10-2-2, we discussed the synthesis of Tebbe s reagent, a bridged Ti methylidene complex. This reagent converts a C=0 group to an alkene in a manner analogous to that of a phosphorus ylide (Wittig reagent).56 Conversion of a carbonyl to a terminal alkene may seem to be of limited utility until one realizes that, unlike phosphorus ylides that react only with aldehydes and ketones, Tebbe s... 

Phosphorus ylides are metal-free carbon nucleophiles that provide irreversible reactions and have been shown to react with support-bound aldehydes. DoUe et al. have reported such a transformation using 4 equiv. of the Wittig reagent in THF [382]. 

The Wittig reaction begins with the preparation of a phosphorus ylide (a Wittig reagent). Figure 10-29 illustrates to formation of atypical phosphorus ylide by an SN2 mechanism, in this case, methylenetriphenylphosphine. 

---