Di-Ylids

Hexaphenylcarbodiphosphorane can also be obtained by reacting triphenylphosphine with carbon tetrachloride in a polar solvent according to scheme. 

Methylene trimethylphosphorane reacts with trimethyldifluorophosphorane to give a covalent ylid-type compound, mp = 74°C, which is soluble in benzene (6.426). According to NMR data, this solution contains equivalent P nuclei, even at low temperature. This has been taken to indicate the presence of a fluxional-type molecule in which there is a rapid site interchange of the F atoms as shown in (6.439) and (Chapter 3.2). 

2Me3P=CH2 -H MejPFj Me3P=CH-PMe3F o FMe3P-CH=PMc3 -t- Mc4PF (6.439) 

Immediate reaction occurs with methylene chloride to give a ylid phosphonium salt (6.440), and if the fluxional fluorine compound is heated with sodinm hydride, hexamethylcarbodiphosphorane 

Ylids react with trivalent boron compounds to give zwitterions. 

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Further reports have appeared on the reaction of trivalent phosphorus compounds with acetylene dicarboxylates. In the first, alkyl diphenylphosphinites (e.g.57) are shown to react with dialkylacetylene dicarboxylates (e.g.58) in the presence of carbon dioxide to form 1,2-oxaphosphol-3-enes (e.g.59) which in the presence of excess phosphinite decompose via (60) to give di-ylids (e.g.61). On the other hand, the phosphoranes (62) from phosphonites and phosphites react with a further phosphorus component to give the ylids (63) which are readily converted by treatment with alcohol into phosphonates (65) apparently via ketene intermediates (64) as evidenced by and isotopic tracer studies. ... 

The parent diphosphinines (Table 6.22) are unknown, and comparatively few derivatives have up to now been characterised. Worthy of note are the 1,4 diphosphoniacyclohexadienes. These di-ylid compounds can be made by reacting ethynyldiphenylphosphines with HBr in acetic acid. Structure analyses of several compounds of this type have shown they are based on flat six-membered rings with rather short C=C distances, thus indicating formula (6.893) in which little or no electron delocalisation occurs around the ring [72,73]. 

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

Zugravescu et al. have reacted the quinoxaline ylid 455 with DMAD and obtained the 1,3-cycloaddition-oxidation product 456.433 They also claim the preparation of 461 from quinoxaline di-JV-oxide (460),434 but isomeric structures do not seem excluded. The quinoxaline imine 457 with DMAD and EP gives 458 and 459, respectively.431... 

An original observation was made with the sterically hindered 2,2,4,4-tetramethyl-3-thioxocyclobutanone and arylazides [254]. Dispiro-l,3,4-di-thiazoles were obtained in 67-83% yields. Their formation was explained by a 1,3-dipolar cycloaddition, elimination of N2 and formation of a novel thiocarbonyl ylid, which underwent dipolar cycloaddition with cyclobuta-nethione. The other outcome possible for the ylid was cyclisation to a thia-ziridine and sulfur extrusion to produce the imine, as previously reported. 

Phosphine oxide anions are often superior to ylids in olefmation reactions, and the anion of 68, made with lithium di-isopropyl-amide (LDA), has none of the disadvantages of the ylid 67. We have made 41 a range of vinyl ethers 70 this wayc, and as part of a synthesis of stiychnos alkaloids43, we were able41 to convert the acyl indole 71 into the aldehyde 72... 

There is no general solvent that is useful for all reactions, and BTF naturally has its limitations. In addition to the limitations posed by the freezing point, boiling point and chemical stability mentioned before, BTF is not very Lewis-basic and therefore is not a good substitute for reactions that require solvents like ethers, DMF, DMSO, etc. Not surprisingly, ions are not readily dissolved in BTF and many types of anionic reactions do not work well in BTF. For example, attempted deprotonations of esters and ketones with LDA in BTF were not successful. Reaction of diethyl malonate with NaH (5 equiv) and reaction with Mel[72] (6 equiv) in BTF was very heterogeneous and yielded 60% of the di-methylated product, compared to 89% in THF. No reaction was observed if the same malonate anion was used as a nucleophile in a Pd-catalyzed allylic substitution reaction in BTF (see 3.7). Wittig reactions also did not work very well in BTF. The ylid of ethyl triphenyl phosphonium bromide [73] was formed only slowly in BTF, and the characteristic deep red color was never obtained. 

The stabilization of the benzhydryl ylid is expected to be quite high since the related fluorenylid (2) can be isolated as a salt free solid. The high yield of 32 was attributed to hydrogen atom abstraction from the cyclohexene by the diphenylcarbene and subsequent coupling of di-phenylmethyl radicals 46>. 

Initially the trimethylamine contains 6% deuterium and it was concluded that a maximum of 6% of the reaction proceeds thru an ylid path 26>. However, when the reaction is carried to completion the trimethylamine contains 17% trimethylamine-di. In this reaction no substitution products (dimethylalkylamines) were obtained when the hydroxide was dried thoroughly, under high vacuum, but an exchange reaction which incorporates deuterium into the methyl groups must be operating and a concerted exchange would have to involve at least one mole of solvent. However, if ylid formation is proposed to account for the exchange reaction, an a -[3 elimination reaction must not occur. 

Eine interessante Folgereaktion tritt bei der Umsetzung von Di-methyl-oxosulfonium-methylid (1) mit Phenylathinyl-phenylketon (30) (40) ein, die das zu (17) analoge stabile Ylid (31) ergibt. Uber die Reak-tion von (1) mit Acetylencarbonestem wird in anderem Zusammenhang weiter unten berichtet (vgl. B I). 

Bei zahlreichen weiteren Reaktionen von Sulfoniumsalzen und Sulfiden laBt sich das Auftreten von Schwefel-Ylid-Zwischenstufen sinnvoll dis-kutieren Oder sogar wahrscheinlich machen. So deuten Markierungsver-suche auf einen a, p-Mechanismus der Hofmann-Eliminierung bestimm-ter Trialkylsulfoniumsalze unter dem EinfluB starker Basen (29, 30) (vgl. 106). 

Cyclohexanone added in one portion at 25 under Ng to a suspension of di-methylthetin anion (a stable S-ylid prepared from dimethylthetin and NaH-dispersion in dimethyl sulfoxide), stirred 3 hrs. at room temp., and the ethereal soln. of the resulting crude glycidic acid treated with diazomethane glycidic ester. Y 60%. F. e., also cyclopropylcarboxylic acid esters, s. J. Adams, L. Hoffman, and B. M. Trost, J. Org. Chem. 35, 1600 (1970). 

This dynamic behavior is not observed when using blocking ligands like cyclopentadienyl. Dicyclopentadienyl lutetium di-tert-butylphosphonium bis(meth-ylid), prepared from dicyclopentadienyl lutetiurri chloride and lithium di-tert-butylphosphonium bis(methylid) in tetrahydrofuran is a monomeric compound in solution, which crystallizes from toluene free of solvent (Schumann and Reier, 1982a) ... 

E)-a,P-Etbylenecarboxylic acid esters. A mixture of m-nitrobenzaldehyde, 1 eq. methyl bromoacetate, and 1 eq. di- -butyl telluride in THF refluxed for 6 h, then quenched with water - (E)-methyl 3-(m-nitrophenyl)propenoate. Y 89%. The method is superior to those based on telluronium salts or on telluronium ylids (requiring strong base) in that it can be used with base-sensitive compds. F.e. inch a,p-ethylene-ketones and -nitriles, and methods, s. X. Huang et al., J. Org. Chem. 53, 4862-4 (1988). 

Das Ylid 232, das am Ylid-C-Atom kein H-Atom mehr tragt, gibt mit Athylnitrit 230 den Athylather 233 des Di-n-propylketoxims... 

Reactions of carbene complexes with tertiary amines, di-, or trialkylphosphines give ylid-type compounds ... 

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