Vinylphosphine oxides

To control the stereochemistry of 1,3-dipolar cycloaddidon reacdons, chiral auxiliaries are introduced into either the dipole-part or dipolarophile A recent monograph covers this topic extensively ° therefore, only typical examples are presented here. Alkenes employed in asymmetric 1,3-cycloaddidon can be divided into three main groups (1) chiral allyhc alcohols, f2 chiral amines, and Hi chiral vinyl sulfoxides or vinylphosphine oxides. 

A stereoselective radical reaction of the ester of M-hydroxy-2-pyridinethione (see also Sect. 4.1) to chiral vinylphosphine oxides has also been described and moderate to good diastereomeric ratios have been obtained for the compound 112 [70] (Scheme 33). 

Rovis and co-workers have also shown that pre-catalyst 129 is competent with a wide range of Michael acceptors including oc,P-unsaturated aldehydes, amides, nitriles, esters, thioesters, vinylphosphonates and vinylphosphine oxides (Scheme 12.25) [58,60],... 

Similar additions also occurred on vinylphosphine oxides. When the optically active vinylphosphine oxide was used, P-chiral alkylphosphine oxide was obtained with retention of the configuration (Eq. 10.27)60... 

Various -substituted vinylphosphine oxides (14) have been made by the Wittig route, and found to be /raws-isomers.17 The geometry of these oxides is believed to be... 

Shift reagents have been used for the configurational and conformational analysis of cyclic phosphites (34).65 The reagent Eu(fod)3 moved Ha of the vinylphosphine oxide (35) twice as far downfield as the corresponding proton in the spectrum of the... 

Brandi and co-workers (29,30) smdied the 1,3-dipolar cycloadditions of chiral a,p-dialkoxynitrones with vinylphosphine oxides (Scheme 12.8). The reaction of optically active 15 with vinylphosphine oxide 16a gave a 65 14 mixture of the... 

Warren and coworkers have reported an interesting synthesis of nonracemic allenes by reaction of vinylphosphine oxides with aldehydes in the presence of chiral lithium [(R)-l-phenylethyl](benzyl)amide to give hydroxyvinylphosphine oxides in 33-87% yields (0-51% ee) [38]. These products underwent a Horner-Wittig elimination reaction to produce nonracemic allenes. A mechanism similar to the Baylis-Hillman reaction was suggested. 

The complete hydrogenation of vinylphosphine oxide 148 and 149 was achieved in one step by hydrogenation with palladium on carbon catalyst using 5 equiv of hydrogen <2000SC4221> (Equation 33). 

Tavs, P, Esters of aryl- and vinylphosphonic acids, aryl- and vinylphosphinic acids and aryl- and vinylphosphine oxides. Shell, U.S. PatentAppl. DE 1810431, 1970 Chem. Abstr., 13, 77387, 1970. 

The major product obtained by alkylation of the carbanion derived from 2-(dimethylamino)ethylmethylphenylphosphine oxide (66) is (67) rather than (68), while alkylation of the carbanion derived from ethylmethylphenylphosphine oxide (70) takes place exclusively at the methyl group.33 The former reaction provides a useful synthesis of appropriately alkylated vinylphosphine oxides (69) which are not otherwise easily prepared (Scheme 12). The N-silylated nitrile imines (72) have been prepared in solution by silylation of carbanions (71) of diazomethylphosphine sulphides.34 At room temperature compounds (72) rearrange to the isomeric diazo compounds (73). 

Pyrazoles (38) are formed in good yields by the dipolar addition of A -phenylsydnone to diphenyl(prop-l-ynyl)phosphine oxide at high temperatures. similar additions of diazodiphenylmethane to a series of vinylphosphine oxides result in the formation of 1-pyrazolines (39), which... 

A new synthesis of vinylphosphine oxides is available from the addition of secondary phosphine oxides to enol acetates to give (43), followed by thermolytic... 

Allylic diphenylphosphine oxides undergo 1,3-dipolar cycloadditions with nitrile oxides to give A -isoxazolines (70) with ann -preferred stereoselectivities of up to 5 1.37 Separate reduction of y -and anti-(70) to the hydroxy amines (71), followed by Wittig-Horner elimination provides stereoselective syntheses of the homoallylic amines (72) (Scheme 9). A study of the effect of substituents on phosphorus on the diastereoselectivity in the cycloaddition of nitrones to vinylphosphine oxides (73) and sulphides (74) has been reported.38 In certain cases diastereoselectivities of >90% were achieved. 

In reactions of chiral vinylsulfoxides, " absolute exo selectivity and high diastereoselectivities were obtained using cyclic nitrones. The cycloaddition of nitrones to chiral vinylphosphine oxides was found to proceed with high endo/exo selectivities and moderate diastereoselectivities. ... 

Oliana M, King F, Horton PN, Hursthouse MB, Hii KK (2006) Practical synthesis of chiral vinylphosphine oxides by direct nucleophilic substitution. Stereodivergent synthesis of aminophosphine ligands. J Org Chem 71 2472-2479... 

Pietrusiewicz and co-workers used optically pure vinylphosphine oxides in the synthesis of substituted derivatives by alkene cross-metathesis (CM), by (achiral) Grubbs and Hoveyda-type ruthenium systems (Scheme 6.47). 

Phosphorus Nucleophiles. Triphenylphosphine is an effective nucleophile for reacting with the bridged sulfonium ion in high yield. The phosphonium salts generated eliminate MeSH upon reaction with base, such as l,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a synthesis of vinylphosphonium salts. If NaOH is used, a vinylphosphine oxide is generated. 

Vinylic phosphate (192) has been reported to react as Michael acceptor with alcohols in basic catalytic conditions to afford, in the case of ethylene glycol, the expected adduct (193). Under similar conditions, the hydroxymethylphosphine oxide (194), used as alcoholic reagent, loses formaldehyde and the salt (195) thus generated adds to vinylphosphine oxide (192) in a Michael fashion to produce 1,2-diphosphosphine oxide (196). 4... 

Water-soluble phosphines, such as 3,3, 3"-phosphanetriyltris(benzenesul-fonic acid) (TPPTS) or m-monosulfonate, give quantitatively the water-soluble phosphonium salts when reacted with a,p-unsaturated acids in water (Larpent and Patin, 1988). They also react with activated alkynes, affording vinylphosphonium salts, vinylphosphine oxides or alkenes depending on the pH of the aqueous solution (Larpent et ai, 1990). 

A cross-couphng approach has been used to functionalize chiral cycloalkenyl substrates in order to prepare enantiopure chiral phosphine precursors (Scheme 4.279) [443]. The catalyst system used cesium carbonate as the base and afforded excellent yields of the vinylphosphine oxide after oxidation with hydrogen peroxide. No scrambling of the neighboring chiral centers was reported. 

SCHEME 4.279 Synthesis of functionalized vinylphosphine oxides through cross-coupling [443],... 

SCHEME 4.280 Synthesis of a chiral phosphine from a vinylphosphine oxide [444]. 

Gem-dibromoalkenes can be converted into vinylphosphine oxides (Scheme 4.296) [462]. Nickel bromide was used as the catalyst in this reaction along with 2,2-bipyridine as the solubilizing/stabilizing ligand. As with many of the other systems described in this section, the chemistry was highly regioselective however, the process consistently generated mixtures of stereoisomers. The chemistry predominately formed the fi-isomer however, the Z-isomer was still formed in most cases. 

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