Arsonium ylides structure

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... 

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. 

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. 

The first account of the preparation of an arsonium ylide (1) was published more than ninety years ago (equation 1), although the correct ylide structure for the product was not provided for nearly half a century. ... 

Arsonium ylides may be represented as hybrids of pentacovalent arsenic (2) and dipolar (3) structures. 

X-ray crystallographic structure determinations have been carried out on a monoben-zoyP and two pentafluoropropionyl arsonium ylides " , on two arsonium cyclopen-tadienylides (e.g. 11)26-28 three arsonium ylides each bearing two electron-... 

Semi-stabilized arsonium ylides are intermediate in behaviour between stable and reactive ylides, and may provide alkenes and/or epoxides " °. In these cases factors such as the substituent groups on arsenic, and the nature of the solvent and of the base, may become important in determining the nature of the product this will be considered in more detail later (Section V.A.4). Small changes in the structure of the ylidic moiety may also have a marked effect for example, whereas triphenylarsonium jS-napththylmethylide reacts to give epoxide, the presence of a bromine atom at the adjacent a-position of the naphthalene ring results instead in the formation of alkenes . ... 

Among the heavy main group elements arsenic has received the most attention. Arsonium ylides react with carbonyl compounds to yield either the alkenes or epoxides, depending upon the structure of the ylide and the reaction conditions. )espite their toxicity, arsenic compounds can be handled safely. 

The structure determination of the arsonium ylide triphenylarsonium 2-acetyl-3,4,5-triphenylcyclopentadienide shows that the arsenic co-ordination... 

However, the electronic spectra of the stibonium ylides were very similar to those of their arsonium analogues, both in solution and in the solid state, and their dipole moments were almost the same, indicating an overall similarity in the electronic structure of the two... 

The bismuthonium acyl- and sulphonyl-ylides have a completely different appearance and electronic spectra, all of them being yellowish in colour. This is because in their cases, as in those of similar arsonium and stibonium ylides, interaction between an oxygen atom and the bismuth atom is possible, leading to structures such as 48 in accord with this... 

The analogous mixed arsonium-iodonium ylides (see structure 442 below in Figure 2.16) were synthesized using a similar procedure [574]. Preparation of hetaryl-substituted phosphonium-iodonium ylides was also reported [575]. 

Various types of phosphorus reagents have been employed for asymmetric transformations of carbonyl compounds into alkenes [2, 4, 7-11]. Depending upon the structure of these reagents, different reaction names are given [3]. Phosphonium ylides and phosphine oxide are particularly popular, and are referred to as Wittig and Horner reagents, respectively. On the other hand, phosphonates and other phosphonic acid derivatives are termed Horner-Wadsworth-Emmons (HWE) reagents. In recent years, arsonium derivatives have often been used for similar reactions, and they are also covered herein. 

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