Phosphorus ylides oxidation

The phosphorus ylides of the Wittig reaction can be replaced by trimethylsilylmethyl-carbanions (Peterson reaction). These silylated carbanions add to carbonyl groups and can easily be eliminated with base to give olefins. The only by-products are volatile silanols. They are more easily removed than the phosphine oxides or phosphates of the more conventional Wittig or Homer reactions (D.J. Peterson, 1968). 

The reaction of an alkylidene phosphorane 1 (i.e. a phosphorus ylide) with an aldehyde or ketone 2 to yield an alkene 3 (i.e. an olefin) and a phosphine oxide 4, is called the Wittig reaction or Wittig olefination reaction. ... 

Due to the presence of a heterocumulene unit, sulphines may be considered as a group of compounds which are able to undergo cycloaddition reactions. Reaction of sulphines with enamines and phosphorus ylides reported by Sheppard217 and Trippett218 and their coworkers may be considered formally as an example of [2 + 2] cycloaddition. In fact, Sheppard and Dickman217 obtained a 1 1 adduct from thiofluorenone S-oxide and 1-morpholinocyclohexene to which they assigned the dipolar sulphoxide structure 168. 

This reaction may be visualized as proceeding by nucleophilic attack of tervalent phosphorus at the carbonyl group to give an intermediate such as (15). The structure of (16) was deduced from the fact that it was hydrolysed to the known phosphine oxide (17). Methylenephosphoranes (phosphorus ylides) may also be converted into monophosphazenes by reaction with benzonitrile ... 

Trzcinskabancroft, B., Knachel, H., Dudis, D., Delord, T.J. and Marler, D.O. (1985) Experimental And Theoretical-Studies Of Dinudear Gold(I) And Gold(II) Phosphorus Ylide Complexes - Oxidative Addition, Halide Exchange, And Structural-Properties Including The Crystal And Molecular-Structures Of [Au (CH2)2PPh2]2 And [Au(CH2)2PPh2]2(CH3) Bri. Journal of the American Chemical Society, 107(24), 6908-6915. 

The second class of benzo-fused heterocycles accessible from benzofuroxans are benzimidazole oxides. In this case only one carbon from the co-reactant is incorporated in the product. With primary nitroalkanes 2-substituted l-hydroxybenzimidazole-3-oxides (46) are formed via displacement of nitrite, and / -sulfones behave similarly. The nitrile group of a-cyanoacetamides is likewise eliminated to alford 2-amide derivatives (46 R = CONRjX and the corresponding esters are formed in addition to the expected quinoxaline dioxides from acetoacetate esters. Under similar conditions secondary nitroalkyl compounds afford 2,2-disubstituted 2//-benzimidazole-1,3-dioxides (47). Benzimidazoles can also result from reaction of benzofuroxans with phosphorus ylides <86T3631>, nitrones (85H(23)1625>, and diazo compounds <75TL3577>. 

It has recently been found that oxetane reacts with phosphorus ylides in a manner similar to ethylene oxide. Trimethylmethylenephosphorane and oxetane give the six-membered heterocyclic compound 2,2,2-trimethyl-l-oxa-2-phospholane in 49% yield (equation 45). The cyclic ylides (46a,b) give 39-47% yields of the corresponding spirobicyclic oxaphos-phoranes. An NMR study showed these compounds to be fluxional as a result of turnstile pseudorotation (79CB501). 

The 1,7-electrocyclization of nitrile imines 47 has been proposed as a key step in the conversion of the stable phosphorus ylides 45 to pyrazolo[4,3-d] [2,3]benzodiazepines 48, upon refluxing in xylene (Scheme 16). Ringopening of the triazoles 45 and recyclization is postulated to give the pyra-zoles 46. Migration of the triphenylphosphine group, followed by the elimination of triphenylphosphine oxide, would then give the nitrile imine 47 (95TL5637). 

In the first step a Wittig reaction" is used to transform the aldehyde into a terminal olefin. This requires initial preparation of a quaternary phosphonium salt. The latter is then deprotonated with sodium amide to give phosphorus ylide 46, which after nucleophilic attack on aldehyde 12 leads to the oxaphosphetane intermediate 47. This intermediate in turn decomposes into olefin 48 and triphenylphosphine oxide. 

In a paper edited in 1953, concerned with the preparation of the stereoisomeric forms of pentaphenylphosphorus, Wittig and GeiBler described the reaction of methylene-triphenylphosphorane 1 and benzophenone 2, forming 1,1-diphenylethylene 3 and triphenylphosphine oxide 4 (Scheme 1). Soon afterwards, it could be demonstrated that alkylidenephosphoranes (phosphine alkylenes, phosphorus ylides) generally react with carbonyl compounds such as aldehydes and ketones to give alkenes with the formation of phosphine oxide 1,2). 

Canthaxanthine (53) is to be regarded as an oxidative metabolite of P-carotene (1). In its industrial production, 4,4 -diacetoxy-p-carotene (52) is used as a starting compound, being hydrolyzed and oxidized 51). This compound, in turn, is obtained by the dimerization of 4-acetoxy-retinal or its phosphorus ylide (51), according to one of the methods described above48. The reaction of 4-oxo-Cls-phosphonium salt (54) with C10 dialdehyde (22) likewise leads to canthaxanthine (53)48b). In a further production process, P-carotene (1) is directly oxidized with chlorate, under catalysis with iodine 49). 

Compound 1295 undergoes a smooth reaction in boiling THE to produce triphenylphosphine oxide and l-(tri-fluoromethyl)-3/f-pyrrolizines 1296 that may be considered as a product of an intramolecular Wittig reaction (Scheme 247) <2006ARK55>. The tautomeric l//-pyrrolizine 1297 was not formed. When phosphorus ylides containing the trichloromethyl group 1298 were heated in THE the expected pyrrolizine 1299 was not formed, and the 2,2,2-trichloro-l-(l//-pyrrol-2-yl)ethanone 1300, dialkyl 2-butynedioate and triphenylphosphine were obtained instead (Scheme 248). 

Phosphorus ylide reacts with aldehyde or ketone to form an intermediate betaine A, which collapsed into oxaphosphetane B. Elimination of triphenylphosphine oxide yields alkene (Scheme 3.31) (also see section 4.3.1). 

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