Alkyl halides with triphenylphosphine

An aldehyde or ketone reacts with a phosphorus ylide to yield an alkene in which the oxygen atom of the carbonyl reactant is replaced by the =0 2 of the ylide. Preparation of the phosphorus ylide itself usually involves reaction of a primary alkyl halide with triphenylphosphine, so the ylide is typically primary, RCH = P Ph)3-This means that the disubstituted alkene carbon in the product comes from the carbonyl reactant, while the monosubstituted alkene carbon comes from the ylicle. 

Ylides are prepared by the reaction of an alkyl halide with triphenylphosphine, followed by treatment with strong base. 2-Bromobutane is the alkyl halide needed in this case. 

The phosphorus ylides necessary for Wittig reaction are easily prepar by Siy-2 reaction of primary (and some. secondary) alkyl halides with phenylphosphine, followed by treatment with base. Triphenylphosphin ... 

Phosphorus ylides are prepared from a nucleophilic substitution reaction between alkyl halides and triphenylphosphine (PPh3). The resulting alkyltriphenylphosphonium salt is then deprotonated by reaction with a strong base (e.g. BuLi) to form the ylide. 

The phosphonium ylide needed for a particular synthesis is obtained by an Sn2 reaction between triphenylphosphine and an alkyl halide with the appropriate number of carbon atoms. A proton on the carbon adjacent to the positively charged phosphorus atom is sufficiently acidic (p/fa = 35) to be removed by a strong base such as butyl-lithium (Section 12.11). 

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. 

Phosphorus ylides like 1 can be prepared by various routes. The most common route is the reaction of triphenylphosphine 5 with an alkyl halide 6 to give a triphenylphosphonium salt 7, and treatment of that salt with a base to give the corresponding ylide 1 ... 

Triphenylphosphine reacts with alkyl halides to form alkyltriphenylphosphonium salts. Upon reaction with strong bases, the salts release a proton to form an ylide (alkylidenetriphenylphosphorane), which is capable of reacting with aldehydes or ketones providing an unambiguous route to olefins. Since there are virtually no... 

Triphenylphosphine. reaction with alkyl halides, 721 Triple bond, electronic structure... 

It is possible to replace one isocyanide by triphenylphosphine, or to replace two isocyanides with diphos, giving phosphine analogues of these complexes. These species are not available from analogous reactions of phosphine-palladium(O) and (II) complexes. Reactions with active alkyl halides proceeds with oxidation nitric oxide also oxidizes these complexes. [Eqs. (31, 32)]. 

Wittig reactions are versatile and useful for preparing alkenes, under mild conditions, where the position of the double bond is known unambiguously. The reaction involves the facile formation of a phosphonium salt from an alkyl halide and a phosphine. In the presence of base this loses HX to form an ylide (Scheme 1.15). This highly polar ylide reacts with a carbonyl compound to give an alkene and a stoichiometric amount of a phosphine oxide, usually triphenylphosphine oxide. 

A convenient one-pot procedure for the conversion of alcohols into primary amines has been reported. The alcohol is converted into the corresponding alkyl halide by the action of bromotrichloromethane/triphenylphosphine and the product is treated successively with sodium azide, triethyl phosphite, hydrochloric acid and sodium hydroxide (equation 20)55, cf. equation 14. 

Competitive lithiation cannot occur with monocyclic compounds, and clean a-lithiation was observed with the rhenium bis-(triphenylphosphine) dihydro complex at -78°C (Scheme 13) [89JOM(362)C31 90H(31)383]. So far, only reaction with alkyl halides has been reported, but presumably other electrophiles would react similarly. 

Halogenations with dihalotriphenylphosphoranes have been reviewed briefly by Fieser and Fieser.4 Dibromotriphenylphos-phorane appears to have been studied somewhat more than the dichloro compound, but both reagents effectively convert alcohols to alkyl halides, carboxylic acids and esters to acid halides, etc. The reaction of 1,2-epoxycyclohexane with dibromotriphenylphos-phorane under conditions similar to those described here gives a mixture of cis- and trans-1,2-dibromocyclohexanes. A reagent prepared from triphenylphosphine and carbon tetrachloride has been used for similar transformations.5... 

The phosphonium salts derived from an o -hydroxybenzyl halide and triphenylphosphine react with a variety of a-halogenated carbonyl compounds in the presence of sodium methoxide to yield chromenes. The speed of the alkylation and the simplicity of the work-up make this an attractive route to 2- and 3-substituted chromenes. 

Quaternisation of triphenylphosphine with an alkyl halide gives a quaternary phosphonium halide (4) which under the influence of a strong base eliminates hydrogen halide to give an alkylidenephosphorane [(5), an ylide]. The latter reacts with an aldehyde or ketone to give first an intermediate betaine (6), which rearranges to the oxaphosphetane (7), which then under the reaction conditions eliminates triphenylphosphine oxide to form an alkene. 

An aldehyde was mixed with solid supported triphenylphosphine oxide (3 equiv.), alkyl halide (4 equiv.), and potassium carbonate (4 equiv.) in methanol (2 ml). The mixture was heated at 150° for 5 min. The residue was filtered through a short plug of silica gel and washed. The solution was concentrated and purified by reverse-phase high-performance liquid chromatography (RP-HPLC). 

The reaction of triphenylphosphine and tetrahalomethanes (CC14, CBr4) with alcohols is a ready method to convert an alcohol to the corresponding alkyl halide under mild conditions. The yields are normally high. 

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