Group 13 trihalides, alkylation

Alkyl groups from alkyl aryl telluriums that have a stabilizing nitrogen functionality in the aromatic ring in an orr/zo-position to the tellurium atom are cleaved by bromine, iodine or sulfurylchloride. Aryl tellurium halides or trihalides are produced in these reactions. 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

Intramolecular adducts have also been used as gallium and indium precursor complexes they are synthesized by the alkylation of the group 13 metal trihalide with an appropriate Grignard reagent,89 as shown Figure 20. 

With a functional substituent in the alkyl group, the self-association may be intramolecular. Thus, in the tu-hydroxyalkyltin trihalides, HO(CI I2) SnGI3, when n 3 or 4, the molecules are intramolecularly coordinated, whereas when n = 5, they form a linear polymer.336 Similarly, MeC02(CH2) SnCl3 forms a cyclic monomer when n = 3, but a cyclic dimer when 11 = 2, and an oligomer when n = 4.337... 

Three main structural sub-groups can be recognised alkylaluminium dihalides, dialkylaluminium halides, and trialkyldialuminium trihalides (equimolar complexes of a trialkylaluminium and an aluminium trihalide). While this is generally a very reactive group of compounds, similar in reactivity to trialkylaluminium compounds, increase in size of the alkyl groups present and in the degree of halogen substitution tends to reduce pyrophoricity. 

Alkyl and aryl tellurium trihalides with stabilizing electron-donor groups in the molecule that coordinate to the tellurium atom are not reduced by disodium sulfite3 or hypophosphorous acid4 to ditellurium compounds but only to tellurium monohalides. 

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

Redistribution of substituents tends to be especially facile for halides, hydrides, and alkyls of Groups I—III nontransition elements because these compounds are electron-deficient. Bridging groups are present in many of these compounds. Even in the boron trihalides that are not bridged, a bridged transition state making use of the empty valence shell orbitals is possible, so that redistribution can occur with a relatively low activation energy (113) ... 

The transformation of a carbon-tellurium bond into a carbon-halogen bond can be performed with several types of organotellurium trihalide or diorganotellurium dihalide compounds, in which the organic group is an alkyl, an alkenyl or an aryl substituent. A variety of reaction conditions have been described to realize these transformations, which belong to three main types ... 

Primary, secondary, and tertiary alcohols undergo nucleophilic substitution reactions with HI, HBr, and HCl to form alkyl halides. These are Sn2 reactions in the case of primary alcohols and SnI reactions in the case of secondary and tertiary alcohols. An alcohol can also be converted into an alkyl halide by phosphorus trihalides or thionyl chloride. These reagents convert the alcohol into an intermediate with a leaving group that is readily displaced by a halide ion. 

Triethylsilane can also facilitate the high yielding reductive formation of dialkyl ethers from carbonyls and silyl ethers. For example, the combination of 4-bromobenzaldehyde, trimethylsi-lyl protected benzyl alcohol, and EtsSiH in the presence of catalytic amounts of FeCls will result in the reduction and benzylation of the carbonyl group (eq 32). Similarly, Cu(OTf)2 has been shown to aid EtsSiH in the reductive etherification of variety of carbonyl compounds with w-octyl trimethylsilyl ether to give the alkyl ethers in moderate to good yields. Likewise, TMSOTf catalyzes the conversion of tetrahydrop)ranyl ethers to benzyl ethers with Ets SiH and benzaldehyde, and diphenylmethyl ethers with EtsSiH and diphenylmethyl formate. Symmetrical and unsymmetrical ethers are afforded in good yield from carbonyl compounds with silyl ethers (or alcohols) and EtsSiH catalyzed by bismuth trihalide salts. An intramolecular version of this procedure has been nicely applied to the construction of cA-2,6-di- and trisubstituted tetrahydropyrans. ... 

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