Alkylation of anions

Scheme 1.11 provides some examples of alkylation of imine and hydrazone anions. Entries 1 and 2 involve alkylation of anions derived from IV-alkylimines. In Entry 1, two successive alkyl groups are added. In Entry 2, complete regioselectivity... 

In fact, the first isolation ofthe vinylidene pentacarbonyltungsten complexes was reported by Mayr et al. in 1984 [6]. The vinylidene complexes 16 were obtained by the alkylation of anionic pentacarbonyltungsten t-butylacetylide complex 15, obtained by the reaction of [Et4N ] [W(CO)5Cl ] with lithium acetylide, with FS03Me or [Et30 ] [Bp4 ]. Further protonation with CF3SO3H in the presence of Me4N P afforded a unique method for the preparation of carbyne complexes 17 (Scheme 5.4). 

Other carboxylic acids have also been alkylated by this method8, and it has even been extended to the alkylation of anions generated from alkyl-substituted benzoic acids9. The reaction of... 

A7-Acyl derivatives of heterocycles can often be quatemized by hard alkylating agents, such as trialkyloxonium fluoroborates406 or methyl fluorosulfonate.364 The quaternary salt is not usually isolated, but N-alkylated derivatives are obtained whose structures are generally different from those obtained by alkylation of anions (Sections IV,C,2). This method, due to Olofson and Kendall,406 has been used with success in azapentalenes [Eqs. (34) and (35)1, where the products 384 and 385 are different from those obtained by alkylation of the anions 361 and 364, respectively (Scheme 16). 

With benzyl, allyl, and primary alkyl halides the yields are 72-90% they are low with isopropyl iodide (34%) with tert-butyl bromide no reaction occurred. This behavior is consistent with results already reported. Alkylation of anions often give poor results with secondary alkyl halides and no alkylation with tertiary alkyl halides. 

Alkylation of anions is generally described by the classical SN1 and SN2 reactions. In some cases these reaction types are not appropriate and the reaction is better described as an electron-transfer reaction followed by a radical coupling within a solvent cage37 (see Section IV,A). 

Solid-liquid phase-transfer catalyzed alkylation of anions. Aliquat 336 is a particularly effective catalyst for alkylation of carboxylate anions (equation 1). The combination of Bu4NBr and Ti02 is slightly less effective (93% yield).6... 

Alkylation,4 Alkylation of anions of the usual alkoxy carbene complexes is not generally attractive because of low reactivity. However, the anion of dialkylamino chromium carbenes such as 1 (R = H) can be alkylated readily and in a useful yield. 

Sulfolenes are versatile 1,3-diene synthons (transformed by refluxing pyridine) which are useful as key intermediates in many natural product syntheses637,638 or as natural products in their own right639. Alkylation of anions of 3-sulfolene has allowed for the introduction of a wide range of substituents in the 2- and 5-positions640. Alkylation of sulfolenes with a,[Pg.738]

Figure 5. Alkylation of anions derived from amides of (l)-ephedrine (32).

Castro A, Spencer TA. Formation and alkylation of anions of bis(methylsulfonyl.methane. J. Org. Chem. 1992 57 3496-3499. 

Pasquini, M. A., Le Goaller, R., Pierre, J. L. Effects of cryptands and activation of bases. V. Action of alkali hydrides on weak acids. II. Alkylation of anions obtained. Tetrahedron 1980, 36, 1223-1226. 

Asymmetric Synthesis via Alkylations of Anions of Masked Carboxylic Acid Derivatives... 

Mulligan, K.J. 1995. Acqueous alkylation of anions for static headspace sampling with analysis by capillary gas chromatography mass spectrometry. Journal of Microcolumn Separations 7 567-573. 

Direct a-alkylation of anions of allylic sulfones 179 gives products 180 from which PhSOj can be eliminated with mild base (MeONa) to give fi-dienes 181. The more usual condensation of sulfones with aldehydes is not necessary and those adducts 169 may eliminate to give vinyl sulfones instead of alkenes.47... 

Asymmetric alkylations of anions of chiral allylamines 5.6 have been performed at -78°C by Ahlbrecht and Enders [1012], These reactions form 2-en-amines with high regio- and stereoselectivities. These enamines are hydrolyzed to generate 3-phenylalkanals 5.7 with a good enantioselectivity (Figure 5.4). The same types of nonracemic aldehydes 5.7 were already obtained with a similar enantioselectivity by Mukaiyama and coworkers [148] via selective alkylation of potassium anions of chiral allyl ethers 5.8 (Figure 5.4). 

On alkylation of anions derived from bislactim ethers of type 1, diastereomeric ratios of... 

Alkylation. The topological analogies outlined in the previous section are substantiated further by considering the chemistry of metal dithienes. We first discuss the alkylation of anionic species. This reaction is equivalent to the alkylation of the hydroquinone dianion and aflFords members of a class of new coordination compounds (14). With simple alkyl halides the d metal dithiene dianions aflFord the 1,4-S-dialkylderiva-tives (16). With a,a>-dibromoalkanes at high dilution new chelates of type 17 were obtained for x = 5-12 (3). With smaller values of x or... 

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