Organometallic reagents aromatic substitutions using

Aromatic Substitutions Using Organometallic Reagents 790 17-14 Addition Reactions of Benzene Derivatives 796 Mechanism 17-9 The Birch Reduction 797 17-15 Side-Chain Reactions of Benzene Derivatives 798... 

Using organometallic reagents to make C-C bonds 17 Nucleophilic substitution at saturated carbon 20 Electrophilic addition to alkenes 22 Electrophilic aromatic substitution 29 Conj ugate Michael addition of enolates 39 Radicals... 

As with preparing allyl complexes, direct reaction of benzyl halides and alkali metals is not a generally useful route to benzylalkali metal compounds due to R-R coupling. Benzylalkali metal compounds can be prepared by (1) addition of organometallic reagents to arylalkenes, (2) cleavage of benzyl ethers (equation 28), (3) transmetallation (equations 29-31), and (4) metallation of methyl substituted aromatics. Q, Q -Bis(trimethylsilyl)benzyl potassium can be prepared by metallation with a mixture of butyllithium and potassium 3-methyl-3-pentanolate in THF. ... 

Work by Kotschy and co-workers showed that reactions of different symmetrical 1,2,4,5-tetrazines with a variety of organometallic reagents furnished, depending upon the combination of reactants, azaphilic addition, reduction or complexation products and not the nucleophilic aromatic substitution products <2004T1991>. On the other hand, Benson et al. reported a smooth displacement of one chlorine substituent in chlorotetrazine 136 using cyanide anion as a soft C-nucleophile (Scheme 36) <2000T1165>. 

The study of aromatic heterocyclic reactivity can be said to have begun with the results of electrophilic substitution processes - these were traditionally the means for the introduction of substitutents onto het-erocylic rings. To a considerable extent, that methodology has been superseded, especially for the introduction of carbon substituents, by methods relying on the formation of organometallic nucleophiles (4.1) and on palladium-catalysed processes (4.2). Nonetheless, the reaction of heterocycles with electrophilic reagents is still extremely useful in many cases, particularly for electron-rich, five-membered heterocycles. 

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