Electron-rich reagents, activation

Electron rich reagents can displace the metal IVb hydride and in the case of optically active complexes this reaction proceeds with retention of configuration. 

Alternatively, the transmetalation can be facilitated by increasing the nucleophilicity of the carbon nucleophile participating in the cross-coupling, which is most often done by increasing the electron density on the metal by coordination of extra anionic ligands. Two distinct approaches to nucleophilic activation are (i) the addition of appropriate Lewis bases to the reaction mixture (nucleophilic catalysis) or (ii) the use of a preformed, electron-rich, organo-metallic reagent with enhanced nucleophilicity. 

Another well-known transformation of carbonyl derivatives is their conversion to pinacols (1,2-diols) via an initial one-electron reduction with highly active metals (such as sodium, magnesium, aluminum, samarium iodide, cerium(III)/ I2, yttrium, low-valent titanium reagents (McMurry coupling), etc.), amines, and electron-rich olefins and aromatics as one-electron donors (D).43 Ketyl formation is rapidly followed by dimerization44 (equation 22). 

As previously discussed, activation of the iridium-phosphoramidite catalyst before addition of the reagents allows less basic nitrogen nucleophiles to be used in iridium-catalyzed allylic substitution reactions [70, 88]. Arylamines, which do not react with allylic carbonates in the presence of the combination of LI and [Ir(COD)Cl]2 as catalyst, form allylic amination products in excellent yields and selectivities when catalyzed by complex la generated in sim (Scheme 15). The scope of the reactions of aromatic amines is broad. Electron-rich and electron-neutral aromatic amines react with allylic carbonates to form allylic amines in high yields and excellent regio- and enantioselectivities as do hindered orlAo-substituted aromatic amines. Electron-poor aromatic amines require higher catalyst loadings, and the products from reactions of these substrates are formed with lower yields and selectivities. 

The electrophilic fluorine of AcOF was also used for aromatic fluorinations. Activated aromatic compounds produced mainly the ortho fluoro derivatives in yields of up to 85%267. The dominant ortho substitution was a result of the addition of AcOF across the most electron-rich region of the aromatic ring. A subsequent spontaneous elimination of AcOH restored the aromaticity, but in cases where this was not possible the resulting cyclohexa-diene reacted very rapidly with the reagent and tars were obtained. Only in certain cases and with careful monitoring could the corresponding adducts be isolated (equation 151.)... 

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