Methylide complexes

From carbodiphosphoranes R3P=C=PR3 and dialkyl-gold (III) halides, cyclic ylide complexes containing four Au-C a-bonds are obtained in a multiple transylidation reaction (equation 24). Related thiophosphorus ylides and sulfonium and sulfoxonium ylides are equally effective in the formation of Au-C a-bonds, and a series of analogous gold-thiophosphonium and sulfoxonium-methylide complexes is available (equations 25-27). ... 

In the initial report by Corey and Chaykovsky, dimethylsulfonium methylide (2) reacted smoothly with benzalaniline to provide an entry to 1,2-diphenylaziridine 67. Franzen and Driesen reported the same reaction with 81% yield for 67. In another example, benzylidene-phenylamine reacted with 2 to produce l-(p-methoxyphenyl)-2-phenylaziridine in 71% yield. The same reaction was also carried out using phase-transfer catalysis conditions.Thus aziridine 68 could be generated consistently in good yield (80-94%). Recently, more complex sulfur ylides have been employed to make more functionalized aziridines, as depicted by the reaction between A -sulfonylimine 69 with diphenylsulfonium 3-(trimethylsilyl)propargylide (70) to afford aziridine 71, along with desilylated aziridine 72. ... 

Romeo, L, Bardaji, M., Concepcion Gimeno, M. and Lagrma, M. (2000) Gold(I) complexes containing the cationic ylide ligand bis (methyldiphenylphosphonio) methylide. Polyhedron, 19(15),... 

Monohomologation of the THF complex of 1-boraadamantane 42 can also be achieved with nucleophilic trimethylsulfoxonium methylide (Scheme 31) and involves a two-step process, consisting of the formation of an ate-complex 83 followed by a [l,2]-migration. Transformation of 42 into 83 is an exothermic reaction. The stmcture of 77 was confirmed by X-ray crystallography <20010L3063, 2003JA12179>. 

The elusive radical cation of pyridine (140) has been obtained by irradiation of pyridine in CFCb at 4 K (79MI20403) and g values and hyperfine coupling constants have been measured for the parent molecule and deuterated derivatives. This species is of cr-type, the odd electron spending most of its time in the N sp2 lone pair orbital. Radical cations and anions of pyridinium bis(alkoxycarbonyl)methylides have been produced in the former case (78CC817) as a cyclopropenone complex, and in the latter by reduction of pyridinium bis(methoxycarbonyl)methylide with sodium (79JMR(35)l7l). The coupling constants in the ESR spectrum of both the radical cation and the anion agree to some extent with simple Huckel MO calculations. 

Methylene trimethylarsorane (the term trimethylarsonium methylide is equally correct) had already been formulated in 1953 by Wittig and Torssell (104) who studied the reaction of tetramethylarsonium salts with organolithium compounds. Although this method cannot be used for the preparation of the salt-free material due to the strong complexation by the lithium cations, it is clear from reactions of the product mixture that the ylide is present in solution. The formation of arsonium salts upon addition of alkyl halides is a typical example ... 

An interesting example of a conversion of a simple ylide into a more complex one is the reaction of triphenylarsonium methylide with a phosphonio derivative of a ketone (equation 30) ... 

The methylene transfer reaction from ylides to ketones has been developed as a convenient synthetic method for obtaining oxiranes [24]. However, the experimental procedure is complex. For example, a THF solution of dimethylsulfonium-methylide (61) is obtained by treatment of trimethylsulfonium iodide (60) with BuLi in THF at 0°C, and after addition of the ketone the mixture is heated at 50-55 °C under nitrogen to yield the oxirane. Throughout the reaction and separation of the product, the organic solvent is essential [25]. 

Charge-transfer complexes with pyridinium cations 82UK185. Cycloaddition reactions of pyridinium N-methylides 82WCH231. Nucleophilic reactions of pyridinium salts 83MI13. 

Methylation Diazomethane-Boron fluoride etherale. Dimethylcopperlithium. Dimethyl-sulfonium methylide. Iodine Methyl iodide. Methyl-(tri-n-butylphosphine) copper complex. Silver perchlorate. Simmons-Smith reagent. Sodium hydride. 

Analogously, interaction with triphenylphosphorus methylide leads to a betaine complex ... 

Banks and coworkers published a series of papers describing the reaction of pyridinium methylides with prefluoroalkenes, perfluoroazaolehns, and trifloroace-tonitrile to produce fluorinated heterocycles, exemplihed by the synthesis of indolizine 74 (Fig. 3.33). Modest yields isolated from complex mixtures were reported. 

The condensation of methyl chloride or bromide to ethylene proceeds by a related mechanistic path involving initial acid-catalyzed dimethylhalonium ion (or related catalyst complex) formation with subsequent proton elimination to a reactive methyl-halonium methylide, which then is readily methylated by excess methyl halide. The ethyl-halonium ion intermediate gives ethylene by jS-elimination (see Scheme 22). 

Dimethyloxysulphonium-methylide reacts with conjugated olejfins to transfer a methylene group and form a cyclopropane. Thus, 1-nitro-prop-l-ene afforded fra/ij-l-nitro-2-methylcyclopropane. Speckamp et fl/. and Tsuge and Shinkai reported similar reactions for a-benzylidenecycloalkanones. The overall more complex reactions with griseofulvin and with isoderritol probably commenced by a similar conjugate addition. Johnson et al have reported that the methylide (59)... 

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