Lead reagents, arylation with

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

Many years later, Fukuhara and Urabe showed that aryl Grignard reagents react with ethyl 2,4-dienoates or 2,4-dienamides, in the presence of iron salts, to give the 1,6-addition products (Scheme 60). This reaction is stereoselective and leads to the (Z)-trisubstituted olefins. 

The successful synthesis of a cyclic oligoplumbane was not reported until 2003. The outcome of reactions of lead(II) halides with aryl Grignard reagents ArMgBr depends on both the steric requirements of the ligand and the reaction conditions. When Ar = 2- Bu-4,5,6-Me3C6H a monomeric plumbylene... 

The reaction of 4-indolyllead triacetate 12 was explored with a number of /3-ketoesters in a study directed toward the total synthesis of welwistatin D (Scheme 3).26 However, while the model ketone derivatives 13 and 15 could be arylated in high yields with lead reagent 12 to give 14 and 16 respectively, the reaction with the more highly substituted welwistatin precursor 17 failed, probably because of the steric hindrance imposed by the methyl and vinyl substituents. 

O-Arylation of alcohols or phenols cannot be performed by copper diacetate-catalyzed reactions using aryllead triacetates as the source of the aryl ligand. However, Dodonov et at. reported that tetraphenyllead reacts with primary and secondary alcohols in the presence of copper diacetate to afford the derived O-phenyl ethers in moderate yields ranging from 1.25 to 1.8 mol. of ether per mole of the lead reagent (Equation (100)). Phenol and tert-butyl alcohol afforded lower yields of the ethers (0.72-0.95 mole per mole of the lead reagent).117... 

Organometallic reagents react with olefinic esters by both 1,2 and 1,4 addition. The latter process leads to saturated esters and is exhibited by diethyl fumarate and to a greater extent by ethylenetetracarboxylic ester, (CjH50jC)jC = C(C0jCjH5)j. These substances are starting materials for the synthesis of alkyl- and aryl-substituted succinic esters. ... 

The number of S- and N-arylations with arylbismuth reagents is relatively limited. The reaction of thiols with pentavalent organobismuth reagents leads mostly to oxidation products and, in some instances, to 5-phenylation. In the case of the nitrogen derivatives, the most efficient arylation by arylbismuth reagents are reactions which are copper-catalysed, and these will be reviewed in a later part of this chapter (see section 6.7). 

The reactivity of ketones towards aryllead (IV) triacetates is quite different from their reactivity towards lead (IV) tetraacetate, with which they are easily functionalised to give the a-acetoxyketones (see section 7.1.1.2). Under the usual conditions for arylation, ketones remain generally unaffected. Only ketone enolates and some specially activated ketones have been successfully arylated with aryllead reagents. 

The method most used for preparation of organolead compounds in the laboratory is treatment of lead(n) chloride with alkyl-, aryl-, or vinyl-Grignard or -lithium reagents, the main products being as shown in the following summary for magnesium 163,395 463 464... 

The carbodiazenylation of olefins is related to the Meerwein arylation. In this case, the aryl radical addition intermediates are not halogenated (as in the original Meerwein protocol) but are trapped with a diazonium salt so as to provide the corresponding radical cation. Reduction finally leads to aryl diazenes. Fe(ll)-salts, Ti(III)chloride and Cu(l)-salts or mixtures of these reducing reagents have been used to conduct carbodiazenylations, some reported examples of which are presented in Equation 13.12 [146]. 

Bidentate l,2-bis(diphenylphosphino)but-l-ene hgands such as 188 are optimal ligands for the reaction of secondary (and primary) alkyhnagnesium reagents with aryl sulfides. As shown for 187, coupling of iPrMgBr leads to 189 with no reduction side product and only minor amounts of the hnear isomer 190 [119] (Scheme 5.42). 

B0C2O is a widely used reagent for introducing protecting groups in peptide synthesis [223, 224]. The reaction of substituted anilines with B0C2O in the presence of a stoichiometric amount of 4-dimethylaminopyridine (DMAP) in an inert solvent (acetonitrile, dichloromefhane, ethyl acetate, tetrahydrofuran, toluene) at room temperature leads to aryl isocyanates in almost quantitative yields within 10 min (Table 4.14) [225]. 

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