Arsenic ylides—

Arsonium ylides were discovered near the turn of the century, but their reactions with carbonyl compounds did not become elucidated until the 1960s. In a broad sense, arsonium ylides are midway in chemical behavior between ylides of phosphorus and those of sulfur. Stabilized arsonium ylides react with carbonyl compounds to afford alkenes, whereas the unstabilized analogs give rise to epoxides. More subtly, the nature of the substituents on either the ylide arsenic or carbon atom can alter the course of the reaction the choice of solvent can exert a similar effect. ... 

The ylides have been classified on the basis of the heteroalom covalently bonded to the carbanion. Accordingly, they can be differentiated into nitrogen ylide (Scheme 2), sulfur ylide Scheme 3, phosphorus ylide Scheme 4, arsenic ylide Scheme 5, antimony ylide (Scheme 6), bismuth ylide (Scheme 7) and thallium ylide (Scheme 8). 

Important literature is available for this type of ylides which are usually thermally stable in the case of phosphorus, arsenic or stilbene C-substituents. This is different for ylides C-substituted by nitrogen atoms which have a destabilizing effect. 

Numerous reactions of carbonyl compounds, alcohols, olefins, etc., with compounds bearing E14=X bonds in which the latter act as direct analogs of phosphorus and arsenic ylides have already been accomplished.17 Recently, an interest in reactivity of compounds with multiple E14-X bonds is increasing due to challenges of important practical applications (see,... 

Reactions of Phosphorus and Arsenic Ylides with Organocyclosilthianes and... 

As mentioned above (see Scheme 1), three main directions of the decomposition of intermediates that formed are possible when phosphorus and arsenic ylides react with compounds bearing C=X bonds 5,6,19,63,64,88 (i) elimination of R3E15=X to form olefins (Wittig type reaction) (ii) retro-Wittig type decomposition and (iii) elimination of R3E15 and formation of three-membered cycles (Corey-Chaykovsky type reaction). According to the data of Erker and coworkers,12,13,51 under kinetic control, the reaction of phosphorus ylides with thiocarbonyl compounds also affords phosphines and thiiranes, whose further transformations lead to olefins and R3PS under thermodynamic control. 

Isomerization of Betaines to Metallated Phosphorus and Arsenic Ylides (Direction A)... 

Decomposition with the elimination of arsenic or phosphorus ylide and formation of silylene (germylene, stannylene) Me2E14, which represents the process inverse to the synthesis of these betaines. 

The thermodynamic data presented in Table XYI are calculated for the temperature T=0K. Note that the entropy factor favors betaine decomposition via directions A and B at higher temperatures. The reactions of organoelement analogs of carbenes with phosphorus and arsenic ylides are yet poorly studied. The presented above results of calculations allow an optimistic prognosis about the possibility of developing a new method for the synthesis of elementaolefins R2E14=CH2 (E14 = Si, Ge, Sn) on the basis of these reactions. 

TABLE 15. Dienes and polyenes with arsenic ylides... 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

The pentavalent triphenylarsenic dihalides are of interest because they present structures that are dependent on the halogenand are convenient sources for the preparation of arsenic ylides. The chemistry of triphenylarsenic difluoride. 

For reviews of arsenic ylides. see Lloyd Gosncy Ormiston Chem. Soc. Rev. 1987,16,45-74 Yaozcng Yanchang Adv. Organomet. Chem. 1982, 20. 115-157. 

For example, see Johnson LaCount Tetrahedron 1960, 9, 130 Bestmann Kratzer Chem. Ber. 1962, 95, 1894. An arsenic ylide has been used in a catalytic version of the Wittig reaction that is. the R AsO product is constantly regenerated to produce more arsenic ylide Shi Wang Wang Huang J. Org. Chem. 1989, 54, 2027. 

For reasons similar to those for the oxides2, studies of the bonding in phosphonium ylides have concentrated on the nature of the P=C bond regarding the following issues (i) the strength of the bond, although in reality this has meant its reactivity (see below) (ii) the exact distribution of the electron density with discussions very similar to those for the oxides and (ii) the difference between phosphorus, nitrogen and (to a lesser extent) arsenic ylides. 

There is a comprehensive review of this area2 so only a few recent developments will be mentioned here. Organoarsenic intramolecular coordination compounds, e.g. (1), have also recently been reviewed,3 and organoarsenic chemistry is reviewed annually.4 There is a review containing 102 references on arsonium ylides.5 The canonical structures of the arsenic ylides are... 

The overlap of carbon p orbitals with arsenic d orbitals is less effective than with the d orbitals of phosphorus, and so the covalent canonical structure is expected to make less of a contribution to the hybrid structure. This has been confirmed in an X-ray study of 2-acetyl-3,4,5-triphenylcyclopentadienetriphenylarsorane.6 Yamamoto and Schmidbaur7 found (13CNMR) that the bonding in arsenic ylides was probably sp3 (cf. phosphorus, which changes from sp3—>sp2), resulting in arsenic pseudotetrahedral geometry (cf. phosphorus ylides, which are planar). 

In addition to sulfoniujn ylides of platinum(II),435 platinum(II) halides of some phenacylides of nitrogen (p-MeC5H4NCHC(0)Ph), phosphorus and arsenic have been prepared.438 The configurations have been elucidated by IR and LH NMR spectroscopy, and it has been found that 2/(195ptHmethine) increases with increasing basicity of the ylide N > As > S > P. 

Reactions of Phosphonic and Arsenic Ylides with Electron Deficient Alkynes and Synthesis of Polyfunctional Fluoroorganics ... 

Chemistry of Fluorine-Containing Phosphine and Arsenic Ylides and Their Salts ... 

Since this discovery a number of binuclear complexes of this type have been isolated, including the arsenic analog of the above (57) and compounds prepared from more exotic ylide precursors (58-60). A polymeric gold(I) complex was obtained by reaction of [AuCl(PMe3)] with the biden-tate ylide CH2=PMe2(CH2)6PMe2=CH2 (60). 

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