Anions, as nucleophiles

Reactions of oxiranyl anions as nucleophilic epoxides 97YGK176. 

In Eq. (3), the unstable methyl diazonium ion decomposes by S l reaction into nitrogen and a methyl cation w hich combines with the anion Z to give CH3—Z. In Eq. (4) an Sk2 reaction occurs. The loss of the nitrogen from CH3—here takes place only wdth the participation of the anion as nucleophile. 

Recently, the solvolyses of l-chloro-l,3,3-triarylallenes 10 (andof 1-butyl-3,3-diphenyl-allenyl chloride) were carried out in the presence of thiocyanate and o-ethyl dithiocar-bonate anions as nucleophiles and found to give the corresponding allenyl derivatives 11 and 12 in good yield (equation 3)18. However, when potassium cyanate was used as a nucleophile, the cyanate ion attacked at the /-position to give the propargyl amines 14 after decarboxylation of the unstable intermediate 13 (equation 4). 

OTHER STABILIZED ANIONS AS NUCLEOPHILES NITRILES AND NITROMETHANE... 

Other stabilized anions as nucleophiles nitriles and nitromethane... 

Alkylation of the a-position of suitable carboxylic acid derivatives may be achieved using the enolate anion as nucleophile in a typical Sn2 reaction (compare Section 10.2). In the example shown, the... 

And what about an alternative product There are two lines of thought, and the most obvious is that the reaction is repeated, since we are using a dibromide as substrate. Alternatively, we could consider one of the other resonance forms of the phenolate anion as nucleophile. This would generate a C-alkylated phenol. In the majority of cases, C-alkylation is not observed, in that the preferred resonance structure has charge on the electronegative oxygen. 

Zhu and coworkers have applied another Ga-based system to the desymmetriza-tion of meso epoxides using acetylide anions as nucleophiles. A complex generated from Mc3Ga and a novel salen provides modest selectivities and yields using phenylacetyhde as the nucleophile ... 

When arenediazonium tetrafluoroborates 7 are not isolated but decomposed in water or aqueous tetrafluoroboric acid, water competes with the tetrafluoroborate anion as nucleophile so that phenols 8 are formed (30- 50 % yield) together with the fluoroarenes 1 (40-55 % yield).179... 

Stabilized enolate anions as nucleophiles formation of carbon-carbon bonds (P condensation)... 

It is known that acetone enolate anion does not react with primary alkyl radicals, and that nitromethane anion is not capable of initiating the SRN1 reactions even under irradiation [99]. Thus, the photo stimulated reactions of 25 with nitromethane anion as nucleophile and acetone enolate anion as entrainment reagent (which enables SRN1 initiation but cannot compete with the coupling of the methylene radical with nitromethane anion after cyclization) render the cyclized products 26 (Sch. 25) [98]. 

Thiophosphite ion, even upon irradiation, only attacks the halogen atom of Me2C(Cl)N02 in an S 2 attack on the halogen188. With azide anion as nucleophile, only low yields of substitution products have been obtained287,288. Much more effective nitrogen--centred nucleophiles in photostimulated reactions with a-halo nitroalkanes are the anions of nitroimidazoles186 and imidazoles187. With the ambident 4(5)-nitroimidazole anion, the 4-isomer is exclusively formed, with no indication of the 5-isomer (equation 72). 

Carbon nucleophiles are very useful species because their reactions with carbon electrophiles result in the formation of carbon—carbon bonds. Section 10.8 introduced acetylide anions as nucleophiles that could be used in Sm2 reactions. These nucleophiles are prepared by reacting 1-alkynes with a strong base such as sodium amide. The relatively acidic hydrogen on the. vp-hybridized carbon is removed in this acid-base reaction ... 

The thiolate anion produced then acts as a nucleophile in the S>j2 reaction, the Sfj2 reaction with a thiolate anion as nucleophile... 

The use of carbonylate anions as nucleophiles in substitution reactions at metals has been used for a long time to prepare other Re-M metal-bonded derivatives, for example, ReCo(CO)9 from [Re(CO)6]+ and [Co(CO)4] and (168) from [ReBr(CO)4]2 and [Fe(C0)4 C(0)R ][NMe4]. ... 

A homoenamine reaction was also observed with hydroxide or hydrogen sulfide (SH ) anion as nucleophile causing a ring opening of 7 to a zwitterion 8, which by proton migration gave the amide 12. ... 

Aminocyclopropanecarbonitriles represent important intermediate products en route to aminocyclopropanecarboxylic acid derivatives. Introduction of the cyano group by nucleophilic substitution into a suitable aminocyclopropane precursor, therefore, is of interest. Thus, the hydroxy- or trimethylsiloxy group of monocyclic A,0-acetals or hemiaminals is readily displaced by the cyanide anion as nucleophile to give products 1. Weak acids catalyze these displacements. ... 

Normally, 5-endo-trig-cyclisations are disfavoured geometrically (Baldwin s rules), however formation of pyrrolidines does take place with tosylamide anion as nucleophile in a situation where 5-ejco-fef-attack at a trihalomethyl group is inhibited electrostatically. ... 

---