Halides, alkyl anions

The major limitation to this reaction is that synthetically acceptable yields are obtained only with methyl halides and primary alkyl halides Acetylide anions are very basic much more basic than hydroxide for example and react with secondary and ter tiary alkyl halides by elimination... 

Alkyl halide Alkyl aryl Halide anion... 

Alkyl halide Lithium Anion radical Lithium cation... 

Helvenston MC, CE Castro (1992) Nickel(l) octaethylisobacteriochlorin anion. An exceptional nucleophile. Reduction and coupling of alkyl halides by anionic and radical processes. A model for factor F-430. JAm Chem Soc 114 8490-8496. 

Amides are weakly nucleophilic and react only slowly with alkyl halides. The anions of amides are substantially more reactive. The classical Gabriel procedure for synthesis of amines from phthalimide is illustrative.58... 

These Sn/Li transmetallations involve nucleophilic attack of an alkyl anion at the tin center. Transmetallations with metal halides on the other hand involve electrophilic attack of the metal at the allylic double bond. 

Sn2 substitution reactions of alkyl halides with hard nucleophiles such as alkyl anions can be achieved most readily with the aid of organocopper chemistry [95]. Sn2 reactions with epoxides and aziridines are also synthetically useful [96]. The... 

This is the case for secondary and tertiary alkyl bromides. If the stability is high, however, as, for example, with primary alkyl bromides, the organo nickel(III) complex is further reduced to an alkyl nickel(II) complex which loses the alkyl group in form of the alkyl anion. An electroinactive Ni(II) species remains. The number of regenerative cycles is consequently low. The structure of the ligand also influences the lifetime of the alkyl nickel(ni) complex thus, a less stable complex is formed in the case of [A,A -ethylene-bis(salicylidene-irainato)]nickel(II) ([Ni(salen)]) as compared with (5,5,7,12,12,14-hexamethyl-l,4,8,ll-tetraazacyclo-tetradecane)nickel(II) ([Ni(teta)] ), and hence the former complex favors the radical pathway even with primary alkyl halides. 

Radical anions are reducing agents and can transfer the extra electron to an alkyl halide. The halide does not remain as a radical ion, but dissociates into a halide ion and an ordinary alkyl radical. If that radical encounters another radical anion, it will be reduced further to alkyl anion.109 Equations 9.58 and 9.59... 

Reaction of alkyl halides with anions in solution, RX(aq) + Y-(aq), - a steady state treatment and comparison with a pre-equilibrium treatment, 202-204, 360-363... 

Magnesium reacts with alkyl halides to form alkyl magnesium bromide salts known as Grignard reagents. As mentioned throughout this book, these species bear nucleophilic carbon atoms. As illustrated using arrow pushing, the alkyl anion adds to the carbonyl and subsequently eliminates methoxide. This addition-elimination process leads to the formation of cyclohexanone. 

In naturally occurring LDHs, the most commonly found interlayer anion is carbonate. In practice, however, there is no significant restriction to the identity of the charge balancing anion that can occupy the interlayer region. Examples include inorganic (such as halides, oxo-anions, silicates and polyoxometalates) as well as organic anions (such as alkyl or aryl carboxylates and sulfonates). 

Most good nucleophiles are basic, becoming protonated and losing their nucleo-philicity in acidic solutions. Halide ions are exceptions, however. Halides are anions of strong acids, so they are weak bases. Solutions of HBr, HC1, or HI contain nucleophilic Br-, Cl-, or I- ions. These acids are commonly used to convert alcohols to the corresponding alkyl halides. 

Incorporation of triethylamine into the reaction medium produced more reduction product presumably due to electron transfer from the triethylamine to the excited alkyl halide. This results in a weakly-bound amine-alkyl halide pair [57]. The alkyl halide radical anion releases X- (Scheme 17). In a related example, it is known that solutions of aliphatic amines in CC14 are unstable to light quickly forming white crystalline precipitates [60]. The initial reaction is formation of a singlet radical pair via excitation of a ground state charge-transfer complex. 

The aryls and alkyls of main group and transition metals that are coordinately unsaturated have Lewis acid character. In alkylations of halides by LiR, in contrast to the use of MgR2, lithium alkylate anions are often formed, for example,... 

The reactions of alkyl halides with anions, Y , in micellar solutions (38) may typify the effects of micelles on nucleophilic substitution... 

Terminal alkynes are weakly acidic. The alkyne hydrogen can he removed by s strong base 9uch ae Na NH.. to yield nn a<%tylide anipn An acetylide anion ads as a nucleophile and can displace a halide ion from a primary alkyl halide in a n alkylation reaction. Acetylide anions are more stable iJian either alkyl anions or vinylic anions because their m ative charge is in a hybrid orbital with 50% s character, allowing the charge to be doser to the nucleus. 

Preparation of acyl and alkyl derivatives of metals may be accomplished by nucleophilic substitution of a halide ion in an acyl or alkyl halide by anionic metal complexes. This reaction also can be used to prepare aryl-metal complexes. Other organic reagents (acetates, tosylates and other species) may also be used as precursors ... 

---