Arsenic nucleophiles

Based on these reactivity studies on azolides, the imidazolides do not represent the most reactive members of the azolide family. In most cases, however, they are sufficiently reactive to undergo nucleophilic reactions leading to the desired products. Due to the easy and economical availability of imidazole, imidazolides are by far the most commonly used azolides for synthetic purposes. If, on the other hand, imidazolides are not sufficiently reactive in a specific case, one of the more active reagents from the arsenal of azolides might be used, as, for example, an azolide derived from a triazole or a tetrazole. 

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). 

In view of the ease with which water attacks an ester of arsenate in water, we wondered if carbon nucleophiles would similarly attack a trialkyl arsenate to form a C—As bond. We (Sparkes and Dixon, unpublished work) therefore treated the sodium salt of diethyl malonate with tripropyl arsenate, and hydrolyzed during workup. Some arsonoacetic acid was formed, but we have not found conditions that give a useful yield. 

Arsenic(III) halides are not salt-like compounds but typically non-metallic halides comparable to, for example, GeCl4 and SC12 besides their predecessors in Group 5, PX3. However AsC13 is not as reactive to nucleophilic attack as is PC13. 

The design of polydentate ligands containing imines has exercised many minds over many years, and imine formation is probably one of the commonest reactions in the synthetic co-ordination chemist s arsenal. Once again, the chelate effect plays an important role in stabilising the co-ordinated products and the majority of imine ligands contain other donor atoms that are also co-ordinated to the metal centre. The above brief discussion of imine formation will have shown that the formation of the imine from amine and carbonyl may be an intra- or intermolecular process. In many cases, the detailed mechanism of the imine formation reaction is not fully understood. In particular, it is not always clear whether the nucleophile is metal-co-ordinated amine or amide. Some intramolecular imine formation reactions at cobalt(m) are known to proceed through amido intermediates. A particularly useful intermediate (5.24) in metal-directed amino acid chemistry is... 

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-... 

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. 

Several non-charged nucleophiles of nitrogen, phosphorus, arsenic, and sulphur displace the phenyliodonio group from iodonium ylides, with formation of new ylides, according to the generalized scheme ... 

It is well known that pentacovalent cyclic phosphorus compounds play an important role as intermediates in reactions involving nucleophilic attack on tetracoordinated phosphorus in biological systems. According to this background it appears to us that it is important to prepare the arsenic derivatives, which are more stable than the corresponding phosphorus compounds and allow the study of their conformation. 

An important use of the traditional Skraup synthesis is to make 6-methoxy-8-nitroquinoline from an aromatic amine with only one free ortho position, glycerol, the usual concentrated sulfuric acid, and the oxidant arsenic pentoxide. Though the reported procedure uses 588 grams of As2Os, which might disconcert many chemists, it works well and the product can be turned into other quinolines by reduction of the nitro group, diazotization, and nucleophilic substitution (Chapter 23). 

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. 

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