Ylides arsonium—

Arsonium Ylides. Arsonium ylides were first prepared by reaction between an arsonium halide and phenyUithium. Thus methyitriphenyiarsonium iodide [1499-33-8], C H gAsI, and phenyUithium give tripbenylarsonium metbylide [19365-61-8], C H yAs ... 

In this case the ylide was not isolated but allowed to react with ben2ophenone to give, after hydrolysis with hydrochloric acid, 1,1-diphenylethylene, diphenylacetaldehyde, and triphenylarsine (160). An excellent method for preparing arsonium ylides involves the reaction between a stable dia2o compound and triphenylarsine in the presence of a copper catalyst such as bis(acetylacetonato)copper(II) (161). Rather than a dia2o compound, an iodonium yhde can be used again a copper catalyst is necessary for an optimum yield of product. An example of the use of a dia2o compound is shown in the formulation of triphenyl arsonium 2,3,4-triphenylcyclopentadienyLide [29629-32-17, C H As ... 

FYedictably, fluoroketones undergo olefination reactions with more reactive arsonium ylides [35] (equation 28). 

Of the quaternary arsonium compounds, methyltriaryl derivatives are important as precursors of arsonium ylides, e.g. 

Such ylides are unstable and react with carbonyl compounds to give both the Wittig product (p. 545) as well as AsPh3 and an epoxide. However, this very reactivity is sometimes an advantage since As ylides often react with carbonyl compounds that are unresponsive to P ylides. Substituted quaternary arsonium compounds are also a useful source of heterocyclic organoarsanes, e.g. thermolysis of 4-(1,7-dibromoheptyl)trimethylarsonium bromide to l-arsabicyclo[3.3.0]octane ... 

Vasishtha [56] also reportedp-acetyl benzylidene triphenyl arsonium ylide radically initiated bulk polymeriza-... 

It is well known that aziridination with allylic ylides is difficult, due to the low reactivity of imines - relative to carbonyl compounds - towards ylide attack, although imines do react with highly reactive sulfur ylides such as Me2S+-CH2-. Dai and coworkers found aziridination with allylic ylides to be possible when the activated imines 22 were treated with allylic sulfonium salts 23 under phase-transfer conditions (Scheme 2.8) [15]. Although the stereoselectivities of the reaction were low, this was the first example of efficient preparation of vinylaziridines by an ylide route. Similar results were obtained with use of arsonium or telluronium salts [16]. The stereoselectivity of aziridination was improved by use of imines activated by a phosphinoyl group [17]. The same group also reported a catalytic sulfonium ylide-mediated aziridination to produce (2-phenylvinyl)aziridines, by treatment of arylsulfonylimines with cinnamyl bromide in the presence of solid K2C03 and catalytic dimethyl sulfide in MeCN [18]. Recently, the synthesis of 3-alkyl-2-vinyl-aziridines by extension of Dai s work was reported [19]. 

Arenediazonium salts also react with stabilized phosphonium, arsonium, pyridinium, and sulfonium ylides (12.111) in acetonitrile, yielding via the azo-onium salt (12.112) the azo-onium ylide (12.113, yellow to red), and in some cases the for-mazane (12.114) (Froyen and Juvvik, 1992). 

Functions [R2Au] are also present in the large family of gold(i) complexes of phosphonium, arsonium, and sulfonium ylides . Section 2.05.6 is dedicated to this class of complexes, where dinuclear compounds with gold in the oxidation state +2 are also common. 

The Cu(I)-catalyzed cyclization for the formation of ethyl ( )-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate 82 has been accomplished starting from propargyl alcohol and ethyl 2-phenylsulfonyl cinnamate. Upon treatment with Pd(0) and phenylvinyl zinc chloride as shown in the following scheme, the methylenetetrahydrofuran 82 can be converted to a 2,3,4-trisubstituted 2,5-dihydrofuran. In this manner, a number of substituents (aryl, vinyl and alkyl) can be introduced to C4 <00EJO1711>. Moderate yields of 2-(a-substituted N-tosyIaminomethyl)-2,5-dihydrofurans can be realized when N-tosylimines are treated with a 4-hydroxy-cis-butenyl arsonium salt or a sulfonium salt in the presence of KOH in acetonitrile. The mechanism is believed to involve a new ylide cyclization process <00T2967>. 

Diarylprolinol ether 30 has also been used to accelerate the cyclopropanation of a,p-unsaturated aldehydes with arsonium ylides with excellent levels of asymmetric induction (95-98% ee) [157]. 

Urns-Epoxides. This unstable ylide (1), when generated as formulated above, reacts with an aliphatic aldehyde at —78° to give a fram-epoxide with almost complete stereoselectivity. The stereochemical selectivity is markedly dependent on the base and also on the counterion of the arsonium salt. Optimum selectivity for the trans-epoxide is obtained with conditions similar to those that induce cis-olefination in Wittig reactions.2 Stereoselection is not so high with aromatic aldehydes. The reagent also reacts with ketones to form trisubstituted epoxides. 

Stereoselectivity of — 50 1 is observed with most aldehydes and with various arsonium ylidcs. Although the method used to prepare 1 is not general, the paper describes general routes to primary and to a-branched 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 catalysts must supply the system with lipophilic cations in order to form, with required anions, ion pairs able to enter nonpolar media. The most typical catalysts are tetraalkyl ammonium (TAA) salts R4N+X, particularly those having at least 16 carbon atoms in the four R groups. Similar lipophilic catalysts are tetraalkylphosphonium and -arsonium or trialkylsulfonium salts, which are less available and usually less stable. They are therefore of negligible practical use. There are a few reports on the use of trialkylamines as catalysts in some two-phase reactions. Usually these amines are qua-ternized by a reactant actually these reactions are catalyzed by TAA salts. More complicated is the generation of dihalocarbenes with trialkylamines. The amines form, with the carbene, an ammonium ylide, which acts as a base in the organic phase. 

However, certain phosphonium ylides, such as those with an electron-withdrawing substituent in the alkylidene moiety, are relatively unreac-tive toward certain substrates such as ketones (22, 77, 95). This led us to consider whether arsonium ylides might be preferable to phosphonium ylides in certain reactions (48, 94). The overlap of the p orbitals of carbon with d orbitals of arsenic is less effective than with d orbitals of phosphorus. Therefore the covalent canonical form (la) should make a smaller contribution to the overall structure of arsonium ylides than to that of the corresponding phosphonium ylides. 

The chemistry of arsonium ylides was first reviewed by Johnson (52) in 1966, by Samaan (78) in 1978, and by Bansal and Sharma (7) recently. In the present chapter, emphasis is placed on studies of the chemistry of arsonium ylides at our Institute and at the University of Science and Technology of Shanghai. However, our work was interrupted and some of our findings were delayed in publication for about 15 years. 

Most of the arsonium ylides reported have been prepared by the so-called salt method, which involves the quatemization of a suitable arsine... 

Although, in principle, any arsonium ylide could be prepared via the slat method as demonstrated above, attempts to prepare a ylide from dimethyldibenzylarsonium salt (4) with ethereal phenyllithium failed. The product of the reaction after quenching with water was stilbene (5). Apparently, a Stevens rearrangement occurred during the reaction (101). 

A facile method for the preparation of a variety of stabilized arsonium ylides in good yield has been developed by the action of active methylene compounds with tertiary arsine oxide or tertiary arsine dihalide. Thus triphenyl-arsine dihalides react with a number of active methylene compounds in the presence of a tertiary amine to afford arsonium ylides (6) (40). The reaction of triphenylarsine oxide with active methylene compounds in the presence of either acetic anhydride or triethylamine-phos-phorus pentoxide gave rise to arsonium ylides (6) (32, 36. 65, 67). 

In the reversible Wittig reaction, triphenylarsine oxide reacted with electron-deficient acetylene derivatives to form stable ylides. Thus triphenylarsine oxide reacted readily with methyl propiolate, ethyl phenylpropiolate, dimethyl acetylenedicarboxylate, and hexafluoro-2-butyne as well as dicyanoacetylene to give arsonium ylides (12). The reaction temperatures required ranged from -70°C in the case of dicyanoacetylene to 130°C in the case of ethyl phenylpropiolate (15). 

Arsonium ylides have also been prepared from the decomposition of diazonium compounds in the presence of a tertiary arsine. Thus tet-raphenylcyclopentadiene triphenylarsorane (13) was obtained by heating diazotetraphenylcyclopentadiene at its melting point in the presence of triphenylarsine (66). 

This method was extended to different diazonium salts and several arsonium ylides (14) were prepared (23, 32). The reaction is greatly facilitated by the presence of copper, copper-bronze, or copper salts. For example, attempts to prepare the bis(carbethoxy)methylene ylide by thermolysis of diethyl diazomalonate in the presence of triphenylarsine without the presence of a catalyst proved abortive, whereas this ylide was obtained in 61% yield if the reactants were heated at 150°C with copper-bronze (32). 

Arsonium ylides can be represented generally by the canonical forms 31a and 31b. By the application of X-ray diffraction to 2-acetyl-3,4,5-triphenylcyclopentadiene triphenylarsorane, Ferguson and Rendle (21) established that the canonical form 7c makes a significant contribution to the ground state structure. 

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