Ylides, sulphonium

Metal catalysed cyclopropanation using other types of intermediate is also possible. Lithiated tert-butyl alkyl sulphones bring about the cyclopropanation of various nonactivated alkenes under nickel(II) acetylacetonate catalysis (equation 88)131,132. Sulphonium ylides of type 90 react with simple alkenes under copper catalysis to give the corresponding cyclopropane adduct (equation 89)113,134. In this example the ylide (90) is the sulphonium equivalent of ethyl diazoacetate134. 

Sulphonium ylides are in certain cases unstable and they undergo further transformation affording useful final products. In this way allylic sulphides and selenides were used to transfer an alkylthio- or alkylseleno-group onto the a-carbon of / -dicarbonyl compounds in the form of their ylides the sequence of reactions were a transylidation followed by [2,3]-sigmatropic rearrangement. 

Other 1-substituted derivatives, such as sulphonium-ylides (6), have been described as intermediates during exposure to diazo compounds, but none of these has been prepared [9,10]. 

Reactivities of arsonium ylides compared to those of phosphonium and sulphonium ylides... 

The reactions of a series of arsonium ylides with p-nitrobenzaldehyde have been shown to be first order for each reagent and there is a general tendency for the more basic ylides to be the more reactive" ". The correlation is not, however, complete, since factors other than basicity, e.g. steric, and interactions between ylidic substituents and the arsenic atom, also affect the reactivity " , but as a generalization it is largely valid and also must be a significant factor in the greater reactivity of arsonium compared to phosphonium and sulphonium ylides. A fair correlation has also been noted between the chemical shift of the signal from the methine proton in a series of ylides and their rates of reaction with p-nitrobenzaldehyde" ". ... 

Reactions of arsonium ylides with carbonyl compounds take place much more readily than with phosphonium or sulphonium ylides. The nature of the products depends upon the character of the substituents on the ylide carbon atom, where electron-withdrawing substituents favour alkene formation, and of substituents on the arsenic atom, where... 

Ylides may react with nitrosobenzene in a similar fashion to their reactions with carbonyl compounds (equation 12). Sulphonium ylides give nitrones phosphonium... 

Kondo, K., Liu. Y, and Tunemoto, D., Preparation and reaction of sulphonium ylide stabilizes by a phosphinyl substituent, J. Chem. Soc., Perkin Trans. 1, 1279, 1974. 

Thiochroman (177) reacts with diethyl diazomalonate, with copper bronze as a catalyst, to form the sulphonium ylide (178) in high yield. Solvolysis of this in acetic acid gave 2-acetoxythiochroman (179) and thiochroman. ... 

K. Hondo, and M. Takaku A Stable Sulphonium Ylide. Tetrahedron Letters (London) 4, 251 (1965). 

Thermal [2,3] sigmatropic rearrangement of the sulphonium ylide (114) gives a 54% yield of a mixture of four isomeric products, the major (70%) of which is the allenic thioether (115), a species which contains the entire artemisyl carbon skeleton hydrolysis with mercuric chloride then leads to artemisia ketone in 80% yield. The second route involves methallylation of the methyl thioacetal monoxide (116), the unstable intermediate (117) on distillation being transformed into the trienic sulphide (118). The latter species on hydrolysis gives artemisia ketone in 57% yield. 

A standard method for the preparation of arsonium and sulphonium ylides involves the reaction of an arsine oxide or a sulphoxide with a compound having an acidic methylene group in the presence of either acetic anhydride or of a mixture of triethylamine and phosphorus pentoxide. This method has been applied to a number of cyclopentadienes substituted either by phenyl groups [105,131,142] or carbonyl groups [20,142,143], When acetic anhydride is used, acetylation of the cyclopentadiene ring may also take place, e.g. 

Various other fluorenylides, e.g. phosphonium and arsonium derivatives, have been prepared similarly [170-175]. The dimethyl-sulphonium ylide decomposes in a few hours in air but the phosphonium and arsonium ylides are thermally stable. 

Tetraphenylcyclopentadienylides, as shown in the exanqile given, have, in particular, been made from diazotetraphenylcyclopentadiene. By this means pyridinium [60,102,134], phosphonium [52,104,105], arsonium [105,106,134,135], stibonium [107], bismuthonium [108], sulphonium [105,109,113,134], selenonium [114] and telluronium [115] ylides have been prepared. The method is improved by the presence of copper conpounds as catalysts and may then often be carried out in solution [105,134], Thermal decomposition of unsubstituted diazocyclopentadiene has not been used to provide cyclopentadien-ylides but sulphonium ylides have been made by photolytic decomposition in the presence of various sulphides [110,111]. 

Solvatochromism is also seen with unsubstituted cyclopentadien-ylides [118,119,121], not only for pyridinium ylides but also in this case for phosphonium and sulphonium ylides. [125], It has been suggested that this solvatochromism is associated with intramolecular charge transfer [121,125] with the ionic ground-state becoming progressively destabilised, with respect to the excited state, in less polar solvents. 

Reactions with Hides and Gvignard Reagents. Reaction with a phosphonium ylide or a sulphonium ylide led, respectively, to the formation of a-naphthol and an a-pyrone. In each case it was assumed that reaction proceeds xda ketene intermediates [110],... 

As reported earlier by Trost, racemization of chiral sulphonium ylides inhibits their utility for asymmetric cyclopropanations. The rates of racemization of a series of sulphonium acylylide derivatives have now been measured and their ease of racemiza-... 

Further studies of carbene insertion into the C S bond are reported, the authors earlier work on alkyl allyl sulphides, using bis(methoxy-carbonyl)carbene, now being supplemented by a study of the relative tendencies towards C—S insertion and C=C addition for the same substrates with carbethoxycarbene (from ethyl diazoacetate). 1,2-Diphenyl-ethyl phenyl sulphide, PhCH(CHaPh)SPh, is formed by the action of benzyne on dibenzyl sulphide, via the sulphonium ylide. Alkylation at sulphur is one of the best-known reactions of sulphides, and novel syntheses of this type have been reported in which the formation of hydro-quinone sulphonium salts, from quinone and a sulphide in 70% H2SO4 at — 5 to -f 5 and Markownikov addition of a sulphide to an alkene under similar conditions are discussed. 

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