Vinyl phosphine oxides

The more reactive fluoroketones also react with reagents prepared by the action of carbon tetrachloride on a tnalkylphosphine to form a vinyl phosphine oxide [id] (equation 29)... 

Malacria and coworkers reported a vinylation sequence of epoxides by employing vinyl phosphine oxides as a radical trap. The overall sequence relies on the facile elimination of phosphinoyl radicals. With vinyl phosphonates the THF derivatives were obtained (Scheme 22). The reaction works equally well under stoichiometric or catalytic conditions [102,103],... 

An unusual two-component domino Michael/aldol process was described by Tomioka and coworkers in which the initiating step is the formation of an a-lithiated vinyl-phosphine oxide [28] or vinyl phosphate [29]. 

Vinyl phosphine oxides and phosphonates are highly electron-deficient and can undergo conjugate reduction much like their carbonyl counter parts. The group of Andersson has reported an enantioselective reduction of both to yield chiral phosphine oxides and phosphonates (Table 6) [67]. 

Another type of chiral alkene applied in 1,3-dipolar cycloadditions are vinyl groups attached to chiral phosphine oxides or sulfoxides. Brandi et al. (150,151) used chiral vinyl phosphine oxide derivatives as alkenes in 1,3-dipolar cycloadditions with chiral nitrones. This group also studied reactions of achiral nitrones with chiral vinyl phosphine oxide derivatives. Using this type of substrate, fair endo/exo-selectivities were obtained. In reactions involving optically pure vinyl phosphine oxides, diastereofacial selectivities of up to 42% de were obtained. Chiral vinyl... 

Type III (no homodimerization) Acrylonitrile," protected 3° allylamines" Vinyl trialkoxysilanes, vinyl siloxanes 1,1-Disubstituted olefins, " non-bulky trisubstituted olefms, vinyl phosphonates, " vinyl phosphine oxides,phenyl vinyl sulfone, acrylonitrile, 4° allylic carbons (all alkyl substituents), protected 3° allylic alcohols, 7,Aolefm of 2-subst. 1.3- butadienes, 7,Aolefin of electronically deactivated 1.3- butadienes ... 

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. 

Other reactions of allyl- and vinyl-phosphine oxides include a detailed study of their intermolecular cyclization by a Friedel-Crafts-type procedure. In certain cases, the unsaturated oxides are generated in situ from /S-hydroxyalkyl(diphenyl)-phosphine oxides. Examples are given in Scheme 12 for the oxides (54)—(56). Control of double-bond position in the products of acid treatment of the oxides (57) has been achieved by using an organosilicon substituent. Thus simple alkyl... 

However, during the addition of -keto esters onto enals, ytterbium triflate proved to be an efficient catalyst [171] as in the Michael additions of a-nitro esters [172]. Several water-soluble phosphines gave the corresponding phos-phonium salts in good yields when added to a,j9-unsaturated acids [173] or activated alkynes [174]. With alkynes, vinyl phosphine oxides or alkenes were formed depending on the pH of the aqueous solution. Significantly, the reaction of nitroalkanes with buten-2-one is considerably accelerated when going from... 

The sulfone 98 allows a tandem (chapter 36) sequence of remarkable selectivity. The lithium derivative of the allylic phosphine oxide 96 (see chapter 12) adds to the enone 97 to give the lithium enolate 99 trapped by the sulfone 98 to give the complex product 100 in 96% yield the only imperfection in stereochemical control is 3% of the Z-vinyl phosphine oxide.16... 

Lithiated ( )- and (Z)-2-alkenylphosphine oxides and phosphonates react with cyclic enones in a 1,4-conjugate addition manner (Schemes 19 and 20). The ( )- and (Z)-allylic anions react in highly dia-stereoselective fashion to deliver respectively syn and anti vinylic phosphine oxides and phosphonates. Chiral allylphosphonyl anions undergo enantioselective 1,4-addition with cyclic enones of varying... 

Polymerised phosphine oxides are generally much more stable than polymerised phosphines. A high-molecular-weight polymer can be obtained from diphenyl(vinyl)phosphine oxide using either free radical or anionic initiation (12.176). 

Addition to Double Bonds. Compared with other alkylsul-fenylating agents, addition of dimethyl(methylthio)sulfonium trifluoromethanesulfonate to double bonds is less frequently used. Treatment of olefins with the reagent followed by the addition of triphenylphosphine gave 2-methylthioalkylphosphonium salts in high yields, which could be converted into vinylphosphonium salts or vinyl phosphine oxides (eq 9). ... 

Vinyl phosphine oxides. Vinyl phosphine oxides have found wide use as versatile synthetic intermediates in the preparation of various mono- and diphosphine systems." The application of 2b and 6 in CM of vinyl... 

Contrary to facile EIM-CM of terminal olefins (Figure 1), the examples of HM between two electron-deficient olefins are rare, and good elds have only been reported for homodimerization of acrylates and enones." We have found that homodimerization of some vinyl phosphine oxides proceeds with good... 

Figure 7. Cross-metathesis of vinyl phosphine oxides (Ae - COCH3).

---