Arsenic nucleophiles, reactions with

Pyridyl-phosphorus and -arsenic compounds have also been made by nucleophilic displacement reactions with, for example, 3-pyridinediazonium salts (74HC(14-2)489). Organomercury derivatives can be converted into bromides and iodides by standard methods, e.g. Scheme 147 (59JPR(8)156). 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

These organometallic nucleophiles show most of the typical reactions with carbon electrophiles associated with benzenoid Grignard reagents and aryllithiums They also allow the introduction of other metals, and nonmetals, on to the ring, such as mercury, boron, phosphorus, tin, and arsenic (Scheme 104) (see also Section 3.2.3.10.2.5), some of which are of great use as partners in transition metal-catalyzed processes. 

Only a few reports deal with reactions of arsenic and antimony compounds with HFA. Several reports describe insertion of HFA into As—H bonds 43, 72, 155). In contrast to the heavier group IV elements, insertion leads to the formation of 2-arsanoperfluoropropanols 87. This difference can be explained by assuming nucleophilic attack by the arsenic lone pair on the highly electrophilic carbonyl carbon. 

In the reaction with halides of the less electropositive metals such as mercury,79 arsenic,80- 81 antimony,82 and indium,83 a stannane provides nucleophilic hydrogen and gives the new metal hydride (equation 15-27). Free radical inhibitors may be added to repress radical reaction of vinyl reactants. The preparation of vinylmercury hydride by this route involves the unusual use of tributyltin chloride as a solvent (equation 15-28).79 On the other hand, in the reactions of tributyltin hydride with Grignard reagents, RMgX, the hydrogen behaves as an electrophile towards R, and the Sn-Mg bonded compounds are formed.84... 

The rate law for trimethylphosphine exchange indicates a dissociative mechanism. A dissociative mechanism, with rate-limiting breaking of a nickel to terminal arsenic bond, also operates for the reactions of trigonal-bipyramidal [NiX(qas)]+ [qas = tris-(u-diphenylarsinophenyl)arsine] with the nucleophiles CN, NOg, Ns , SCN", I, thiourea, and triphenylphosphine. A preliminary report on a very similar reaction, equation (20), in methanol solution, gives observed rate constants kt and Arb) for the... 

A series of 7-substituted norbornadienes have been synthesized by quenching the 7-norbornadienyl cation with various nucleophiles of sulphur (SMOj), arsenic (AsPhj), and antimony (SbPhg). 7-t-Butylnorbornadiene, prepared by reaction of t-butyl-lithium with 7-t-butoxynorbornadiene, has been transformed to, inter alia, (128) and (129). By a similar route, (20) and related compounds, required for study of their photoelectron spectra, were prepared (Scheme 5). Propenylidene-norbornadienes were accessible by the routes shown in Scheme 6. They provide a novel photochemical synthesis of dihydro-azulenes, azulenes, and of vinylogous heptafulvenes. 

The SRN1 process has proven to be a versatile mechanism for replacing a suitable leaving group by a nucleophile at the ipso position. This reaction affords substitution in nonactivated aromatic (ArX) compounds, with an extensive variety of nucleophiles ( u ) derived from carbon, nitrogen, and oxygen to form new C—C bonds, and from tin, phosphorus, arsenic, antimony, sulfur, selenium, and tellurium to afford new C-heteroatom bonds. 

Ylides are neutral compounds characterized by internally compensating ionic centers, a carbanionic group and a neighboring onium unit, typically localized at phosphorus, arsenic, or sulfur, Ylidic carbanions are strong nucleophiles and show a high affinity for most metals in their various oxidation states. This can be exemplified by the reactions of a simple phosphorus ylide, like trimethylphos-phonium methylide (trimethylmethylenephosphorane), that are now known to lead to organometallic compounds with exceptionally stable carbon-to-metal bonds. 

A publication discussing the uses of reactive arsonium ylides for the stereospecific preparation of epoxides draws attention to the fact that arsonium salts are less readily prepared than phosphonium salts because of the poorer nucleophilicity of arsenic compared to phosphorus, and suggests methods for obtaining them. Primary salts were made from alkyl triflates, while a-branched salts were prepared from alkyldiphenylarsines, obtained from iodo compounds as, for example, in equation 23. Reaction of alkyl halides with arsines to form arsonium salts is also promoted by the presence of silver tetra-fluoroborate . 

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