Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Lithium diphenylphosphide, oxidation

B. From Metallated Phosphines.—Lithium diphenylphosphide and ethylene oxide produce (7), which when added to chlorodibutyl- or chlorodiphenyl-phosphine yields 2-diphenylphosphinoethyl phosphinites (8). [Pg.2]

Triarylphosphines were prepared by the reaction between lithium diphenylphosphide in THF and m-and p-iodotoluene (or the corresponding bromo compounds), 4-bromobiphenyl and p-dibromobenzene in yields of 70-80% (isolated after oxidation, as the phosphine oxides).143 The absence of cine substitution products is a synthetic advantage and would have been taken as a prima facie indication that the displacements are examples of the 5rn1 reaction, had the mechanism been recognized at the time. Operation of the radical ion mechanism in DMSO, or liquid ammonia, in which marginally improved yields are obtained, was confirmed by Swartz and Bunnett,48 but no extension to the scope of the reaction was made. Rossi and coworkers have developed a procedure for one-pot preparation of triarylphosphines starting from elemental phosphorus (Scheme 6).146 As an example of the synthesis of a symmetrical tri-arylphosphine, triphenylphosphine (isolated as its oxide) was obtained in 75% yield, with iodobenzene as the aryl halide (ArX in Scheme 6, steps i-iii only). Unsymmetrical phosphines result from the full sequence of reactions in Scheme 6, and p-anisyldiphenylphosphine (isolated as its oxide) was produced in 55% yield, based on the phosphorus used, when chlorobenzene (ArX) and p-methoxyanisole (AiOC) were used. [Pg.473]

In 1955 Wittig et al. found that triphenylphosphine could induce the deoxygenation of epoxides at 200 Mechanistically, this process probably involves anti opening of the epoxide followed by syn elimination of triphenylphosphine oxide from a betaine intermediate. Accordingly, the reaction proceeds with inversion of stereochemistry, which means that franj-ejjoxides give ci5-alkenes. The systems of bis(di-methylamino)phosphorous acid/butyllithium, o and lithium diphenylphosphide have been examined... [Pg.885]

Olefin inversion.2 Lithium diphenylphosphide in THF opens epoxides stereo-specifically quatemization of the crude product with methyl iodide leads to betaines, which fragment under mild conditions (25°) to give an olefin and methyldiphenyl-phosphine oxide. The product olefins are formed with inversion of stereochemistry relative to the starting epoxide owing to SN2 epoxide opening followed by cis elimination of the phosphine oxide. Thus the oxide of fraus-stilbene (1) is converted into the betaine (2), which at 25° gives cis-stilbene (3) in 95% yield overall. The conversion is stereospecific (> 98%). Similarly cis-stilbene can be converted into franx-stilbene. [Pg.489]

Treatment of epoxides with lithium diphenylphosphide followed by oxidation gives i3-hydroxydiphenylphosphine oxides which can be fragmented to olefins stereospecifically, thus constituting an olefin inversion (Scheme 2). [Pg.9]

Allylic phosphine oxides Wittig-Homer synthesis of 1,3-dienes Allylic phosphine oxides can be prepared by reaction of 2,6-dichlorobenzoates of allylic alcohols with lithium diphenylphosphide followed by oxidation. Thus... [Pg.340]

The first enantiomerically pure chiral representatives of this class of ligands were published by Tani in 1995. °- Enantiomerically pure ditosylate 37, derived from L-threitol, was treated stepwise with lithium diphenylphosphide and with cyclopentadi-enyllithium or indenyllithium to give ligands 38 and 39 in 27% and 31% yield, respectively (Scheme 8). In addition, enantiomerically pure ditosylate 40 was treated with lithium diphenylphosphide, followed by oxidative aqueous workup. Phosphorane 41 was obtained in 65% yield, and subsequent substitution of the second tosyl group by lithium cyclopentadienide gave 42 (60% yield), which was reduced to the desired ligand 43 with trichlorosilane in 50% yield. 43 is described as an air-sensitive colorless oil, which was characterized as its oxide 42. [Pg.6]

Treatment of methyl 6-0-tosyl-2,3,4-tri-0-trimethylsilyl-a-D-glucopyranoside with lithium diphenylphosphide at reflux temperatures (in THF or ether) afforded methyl 6-deoxy-6-diphenylphosphino-a-D-glucopyranoside, whereas at lower temperatures S-0 bond cleavage predominated. Similar treatment applied to methyl 2,3-0-isopropylidene-5,6-di-0-methanesulfonyl-a-D-mannofuranoside gave, after subsequent air oxidation, a mixture of 10 and 11," and a new... [Pg.216]


See other pages where Lithium diphenylphosphide, oxidation is mentioned: [Pg.1341]    [Pg.96]    [Pg.303]    [Pg.586]    [Pg.1518]    [Pg.9]    [Pg.297]    [Pg.1320]    [Pg.1389]    [Pg.90]    [Pg.217]    [Pg.4]    [Pg.8]    [Pg.180]    [Pg.228]    [Pg.339]    [Pg.145]    [Pg.86]    [Pg.46]    [Pg.4]   
See also in sourсe #XX -- [ Pg.90 ]




SEARCH



Diphenylphosphide

Lithium diphenylphosphide

Lithium oxidation

© 2024 chempedia.info