Anionic version

Boron forms a remarkable series of binary compounds with hydrogen—the boranes. These compounds include diborane, B2H6, and more complex compounds such as decaborane, B10H14. Anionic versions of these compounds, the borohydrides, are known the most important is BH4 as sodium borohydride, NaBH4. 

N-Unsubstituted azomethine ylides may be generated thermally (79), and the N-metalated, 2-azaallyl anion versions may be generated by action of nonmetalhc bases such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) on certain imines (80). Although they are assumed to show similar chemical properties, these two species usually show different reaction patterns, as shown in Scheme 11.7, where the regio-and stereoselectivities of the cycloadditions are quite different (24,78-80). Metala-tion of (alkylideneamino)acetonitriles can be performed with metallic bases other than LDA. Thus, butyllithium, ethylmagnesium bromide, and magnesium bromide-diisopropylamide are also effective (78). The N-magnesioazomethine... 

In an elegant approach to gelsemine [238] based on a similar strategy the cationic aza-Cope rearrangement was superseded by a simple Mannich reaction because the twistane skeleton is more highly strained. However, the desired transformation is achievable using the anionic version. 

Note also the radical migration of the benzoyl group from C-2 to C-3, as in the anionic version (Scheme 29). 

Other well-known reactions are those offluorinated olefins with fluoride ion and negatively substituted aromatic compounds leading to the formation of per-fluoroalkylated aromatic compounds The reaction may be considered an anionic version ot a Friedel Crafts process and can result m introduction of one or several perfluoroalkyl substituents [HI] Aromatic substrates include substituted and unsubstituted perfluorobenzenes [131, 212, 213, 214], fluorinated heterocycles [131, 203, 215, 216, 217, 218, 219, 220, 221, 222, 223], perchlonnated heterocycles [224] (equation 44), and other activated aromatic compounds [225] (equation 45) The fluorinated olefins can be linear or cyclic [208] (equation 46)... 

Anionic versions of boranes. The most important borohydride is BH4, as in sodium borohydride, NaBH4, which is produced by the reaction of NaH with BCI3 ... 

When secondary amines are used, an anionic version of the reaction occurs when the amine is deprotonated by -BuLi. 

Several of the anionic versions of these complexes (E ) are excellent candidates to form bridging interactions between metal centers directed at the formation of polynuclear complexes. 

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