Arsoranes—

A. Preparation.—The first reverse Wittig olefin synthesis has been reported. Triphenylphosphine oxide and dicyanoacetylene at 160 °C gave the stable ylide (1 78%) the reaction was reversed at 300 °C. No comparable reaction was observed with a variety of other activated acetylenes but tri phenyl arsine oxide gave the corresponding stable arsoranes with dicyanoacetylene (— 70 °C), methyl propiolate, hexafluorobut-2-yne, dimethyl acetylene dicarboxylate, and ethyl phenylpropiolate (130 °C). 

Table 4 Spirocyclic Arsoranes As—O Bond Lengths and TBP— RP Distortions...

Arsoranes that contain fluoroacyl groups have been obtained by the methods described in the following paragraphs. 

Reactions of carbomethoxymethylene triphenylarsorane with per-fluoroacyl chlorides gave perfluoroacylcarbomethoxymethylene triphenyl-arsoranes (26) (42). 

Johnson and Schubert (56) reported that the H-NMR spectrum of phenacylidene triphenylarsorane showed 20 aryl protons at 8 7.2-8.1 and a single methine proton at 8 4.75. The latter signal was quite broad unless the sample and solvent were perfectly dried, probably because of proton exchange. The I3C-NMR spectra of some arsoranes were also studied (26, 102). The data are listed in Table 1. 

Reaction Products ot Cyanomethylene Triphenyl Arsorane with Various Ketones... 

On the other hand, a number of semistabilized arsoranes reacted with the bulky aldehyde 9-anthraldehyde or ketones 9-anthrone and 2-chloro-9-anthrone to form olefins exclusively, regardless of the base or solvent (sodamide-CeH6 or sodium methoxide-methanol) used (92). 

Acetylmethylene(triphenylphosphine)-arsorane. Crown ethers. Cyanomethylene(triphenylphosphine)-phosphorane. 

In this article the author has been using the traditional ylide-ylene nomenclature as well as the modern phosphorane-arsorane-stiborane formalism. No attempt has been made to discriminate between one or the other of these modalities because it is felt that both offer a sufficiently clear description of at least those species that are derived from the main Group Vb elements. (Fortunately no Nli,s or BiR5 had to be given names.). However, when this procedure was followed with the vanadium, niobium, and tantalum compounds, an interesting problem arose because the authors... 

Thus, 2,2 -biphenylylene-triphenylarsorane 115 could be prepared along two ways, either with 5-phenyldibenzarsole tosylimine 114 and phenyllithium or with triphenylarsine tosylimine 116 and 2,2 -dilithiobiphenyl 121,122). Likewise, the spiro-arsoranes 117, 118 were synthesized in high yields, 118 being rather unstable, probably because of unfavorable steric interactions at the reverse of the benzo-biphenyiylene ligand121). 

Again, for these compounds, names emphasizing the arsorane nature, e.g. bis-2,2 -biphenylylenearylarsorane for 117, or names evaluating more the heterospirocyclic skeleton, e.g. 5 -(4-dimethylaminophenyl)spiro[l 1 H-benzo[b]naphth[2,1 -djarsole-ll,5 -[5 //]dibenzarsole] for 118 are possible. 

All attempts to combine sterically overcrowded alkyl Grignard reagents of the neopenthyl type with the spiroarsonium skeleton 120 led directly to the rearranged structures 126. It is not clear whether these reactions involve the corresponding arsoranes 122i, j as short lived intermediates or whether the nucleophilic attack is directed here from the beginning toward an arene ligand123). 

A fairly stable hexaarylarsenate ion was finally obtained in the form of onium-ate complex 133 when spiroarsonium salt 120-1 was reacted with 2,2 -dilithiobiphenyl in ether. With excess 2,2 -dilithiobiphenyl in tetrahydrofurane the reaction proceeds to the lithium salt of the tris-2,2 -biphenylylenearsenate ion (Li-134) which is also obtained, besides arsoranes 117a, 122a, when 133 is treated with phenyl- or methyllithium. With sodium iodide in acetone onium-ate complex 133 is cleaved into its component salts 120-1 and Na-134. Both alkali metal salts Li,Na-134 are moisture sensitive and react readily with water or alcohols so that the hexacoordinated structure is destroyed and the ring-opened arsorane 135 is produced 30). 

Whereas earlier evidence for a trigonal-bipyramidal structure of pentaphenyl-arsorane and its derivatives could only be deduced indirectly on the basis of X-ray analogy considerations 62,63>, IR-studies126) and not very conclusive 1H-NMR-ex-periments (only one methyl signal for penta-p-tolylarsorane 77)), a more recent crystal structure determination for a solvate of pentaphenylarsorane with one half molecule... 

At 100 °C pentamethylarsorane (/) is quantitatively decomposed to trimethyl-arsine, methane and a little ethylene, thus supporting the assumption of intermediate formation of ylide 148 ethane is only formed in traces131). With water and acids tetramethylarsonium salts are produced m) whereas with alcohols, hydroxylamines and oximes covalent pentacoordinate arsoranes 149 are obtained in which one methyl group has been replaced by the respective electronegative group Y 132,133). 

It might be mentioned in this connection that on the basis of IR-studies it has been concluded that the M(C6H5)4 groups in pentaphenylstiborane, -arsorane and -phosphorane are probably weak electron acceptors146. ... 

Hellwinkel et al. (98) have also carried out an 1H-NMR investigation of some overcrowded asymmetric phosphoranes, arsoranes, and sti-boranes. In XII (R = phenyl or biphenyl), the two different positions are reversibly equilibrated at elevated temperatures. 

Mixing of the arsorane RAs(OMe)4 (R = OMe, Me, or Ph) with the diol compound in a 1 1 molar ratio leads to the formation of monocyclic arsoranes quantitatively only in the case where the diol is pinacol and R = OMe ... 

The oxidation of 2-iodo-l,3,2-diheteroarsolanes by tetrachloro-o-benzo-quinone has been studied by Wieber and Gotz (193). In this reaction the cleavage of the As—I bond occurred with the formation of spirocyclic arsoranes ... 

Mallon and Weiber (128) have prepared spirocyclic arsoranes XXX by the reaction between PhAs(0)(0H)2 or MeAs(OMe)4 with HOXYH (where R = Me, Ph X = CH2CH2, o-Cgl, 2,3-C10H6 Y = S, NH, NMe). Wunderlich (203) determined the crystal structure of... 

---