Cyano anions

Strecker reactions provide one of the most efficient methods for the synthesis of a-amino nitriles, which are useful intermediates in the synthesis of amino acids and nitrogen-containing heterocycles. Although classical Strecker reactions have some limitations, use of trimethylsilyl cyanide (TMSCN) as a cyano anion source provides promising and safer routes to these compounds.133-351 Consequently, we focused our attention on tributyltin cyanide (Bu3SnCN), because Bu3SnCN is stable in water and is also a potential cyano anion source. Indeed, the Strecker-type reactions of aldehydes, amines, and Bu3SnCN proceeded smoothly in water (Eq. 9).1361 It should be noted that no surfactants are required in this reaction. Furthermore, Complete recovery of the toxic tin compounds is also possible in the form of bis(tributyltin) oxide after the reaction is over. Since conversion of bis(tributyltin) oxide to tributyltin cyanide is known in the literature, this procedure provides a solution to the problem associated with toxicity of tin compounds. 

IR spectroscopy has been used to study complex formation in solution and the absorption of complex cyano anions on 200-400 mesh Dowex-A-1 anion exchange resin.8 To complement these studies the Raman spectra have been obtained for solid KAg(CN)2 and for the complex... 

Cyano Anions of Dicoordinated, Tricoordinated, Tetracoordinated, Pentacoordinated, and Hexacoordinated Phosphorus... 

More recently Behrens and co-workers15 were able to prepare the series of monocyano nitrosyl carbonyls by reactions such as equation (1). The Mn° compounds obtained in this work are listed in Table 6. Na[Mn(CN)(CO)3(NO)] dissolves readily in polar solvents such as water, ethanol, acetone or THF, but the solutions, even in the absence of light and air, are unstable. Crystalline salts, which are air stable, were obtained by adding such a solution to an excess of the appropriate cation. The related isonitrile species were prepared by alkylation of the cyano anions with R304. ... 

The nitrato anion [Pt(N03)4]2" can be obtained by treating [Pt(H20)4]2+ with KN03. The cyano anions [M(CN)4]2 of both Pd and Pt are extremely stable with high formation constants. Other square anions are the a alkyls and aryls, of which the perhalogenated anions such as [Pd(C6F5)4]2 and [Pt(C6Cl5)4]2- are most stable. 

An early example involved mononuclear thiomolybdates and excess cyanide (227). In related studies, Muller and co-workers (i 75,228-230) have isolated and characterized a variety of polynuclear cyano anions of Mo(IV) and Mo(III). These complexes feature and jug-thio ligands,... 

The literature offers more examples of facile deprotonations of cyclopropyl nitriles. Boche and coworkers and Ford and Newcomb observed the deprotonation of the nitriles 260 and 261 as well as their alkylation 262 has been deprotonated by Wittig and co workers . Similarly, 263 is easily deprotonated to give the a-cyano anion— in contrast to the corresponding ester 227 which is deprotonated exclusively at C(l) instead Compound 264 also gives the corresponding a-cyano cyclopropyl anion... 

Ion-pair effects, as in the case of the unsubstituted allyl alkali metal compounds 23a-d, do not markedly influence the rotational barriers of the 1,3-diphenylallyl-lithium species 27a-f, although the reason is different 27a-f are solvent-separated ion pairs 36). Addition of HMPT to the THF solution of 27a raises the AG3 c value by 0.9 kcal/mol which corresponds to a rate retardation of 5-6 times. In the case of the methyl-substituted allyl anion 27b HMPT slows down the rate by a factor of only 2-3. With the 2-cyano anion 27c the AG values of the Li+ compound in THF and the Li +, Na+ andK+ species in dimethyl sulfoxide (DMSO) are the same18). In the case of 27e and 27f the rate of the rearrangement is not affected if HMPT or TMEDA are added to the THF solutions. The observations of some solvent dependence in the case of the sterically less hindered 27a and b, but of no effect with the more crowded 27e and f are in line with the general observation that solvent-separated ion pairs are favored with respect to contact ions pairs by increasing steric hindrance 25). Hence, these experimental results could be interpreted to mean that in the case of 27a and b contact ion pairs participate in the allyl anion rearrangement reaction. 

This methodology has been successfully extended to the preparation of cyano-fluoromethylene compounds. Thus the a-fluoro-a-cyano anion (10) generated in situ was trapped with RX [64], R2NCOCI [65], and allylic halide ]66] to afford the adducts in high yields (Scheme 11.42). 

The tricyanohalophosphite anion is formed more readily than the PBr4 anion (Chapter 4.6). The di- and tri-cyano anions exist in the solid state as distorted trigonal bipyramidal and dimeric octahedral configurations, respectively, with lone-pair electrons occupying one coordination site. 

The alkylation of a-cyano anions [49,50] and metal cyanides [49] with organic halides has been among the most popular methods for the preparation of nitriles. Some years ago. Brown et al. [51, 52] showed that the reaction of tri-alkylboranes with chloroacetonitrile gave the corresponding nitriles in good yields. Their results suggest that the alkylation of haloacetonitriles with orga-nometallic compounds would provide an alternative route for the preparation of nitriles by carbon-carbon bond formation. However, no related examples have been reported. 

Compound 3 could be generally prepared by the benzylation of sodioace-tonitrile [60, 61], by the condensation of carbonyl compounds with a-cyano anions [62, 63] followed by a catalytic hydrogenation of 3-arylcinnamonitriles formed, [54] or by the cyanoethylation of aromatic substrates with 3-chloro-propanenitrile or acrylonitrile/hydrogen chloride [53, 64]. However, the first method afforded a mixture of mono- and dibenzylated products. The second method required two reaction steps although the catalytic hydrogenation occurred quantitatively. The last method proceeded with poor regioselectivity when substituted aromatic compounds were employed as substrates. 

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