Carbanion reaction with nitriles

Dithioacetals RCH(SPh)2 and vinylogues [i.e., RCH(SPh)CH=CHSPh] become carbanion equivalents [RCH2] when they are treated with Cp2Ti[P(OEt)j]2 and Mg. Thus, a subsequent reaction with nitriles furnishes ketones. Conjugated dienes and alkenylcyclopropanes are also obtained. ... 

Inductive and resonance stabilization of carbanions derived by proton abstraction from alkyl substituents a to the ring nitrogen in pyrazines and quinoxalines confers a degree of stability on these species comparable with that observed with enolate anions. The resultant carbanions undergo typical condensation reactions with a variety of electrophilic reagents such as aldehydes, ketones, nitriles, diazonium salts, etc., which makes them of considerable preparative importance. 

Enaminosulphoxides 459 have been obtained in the reaction of the carbanion of methyl methylthiomethyl sulphoxide 324 with nitriles. This procedure has been applied for converting nitriles into a-aminoacids 460527 and a-ketoacids 461528 (equation 275). 

Treatment of the carbanion derived from 94 with nitriles was shown to give enaminesulfoxides 136, which can be converted to a-ketoesters or a-ketoacylamides185, besides the ester of JV-acetylamino acid 137. Using this reaction, the methyl ester of dl-JV-acetyl-5-hydroxytryprophane 138 was synthesized186. 

The catalytic conditions (aqueous concentrated sodium hydroxide and tetraalkylammonium catalyst) are very useful in generating dihalo-carbenes from the corresponding haloforms. Dichlorocarbene thus generated reacts with alkenes to give high yields of dichlorocyclopropane derivatives,16 even in cases where other methods have failed,17 and with some hydrocarbons to yield dicholromethyl derivatives.18 Similar conditions are suited for the formation and reactions of dibromocar-benc,19 bromofluoro- and chlorofluorocarbene,20 and chlorothiophenoxy carbene,21 as well as the Michael addition of trichloromethyl carbanion to unsaturated nitriles, esters, and sulfones.22... 

Addition of C-nucleophiles to nitrile oxides is of special interest. There are examples of reactions with both carbanions and neutral carbon nucleophiles. To the former group belong reactions of nitrile oxides with organometallic... 

Decarboxylation of 1,3-dimethylorotic acid in the presence of benzyl bromide yields 6-benzyl-1,3-dimethyluracil and presumably involves a C(6) centered nucleophilic intermediate which could nonetheless have either a carbene or ylide structure. Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry has been used to explore the gas-phase reactions of methyl nitrate with anions from active methylene compounds anions of aliphatic ketones and nitriles react by the 5n2 mechanism and Fco reactions yielding N02 ions are also observed nitronate ions are formed on reaction with the carbanions derived from toluenes and methylpyridines. 

Problem 17.37 The C of the —C=N group is an electrophilic site capable of being attacked by a carbanion. Show how nitriles like CHjCH C N undergo an aldol-type condensation (Thorpe reaction) with hindered bases. M... 

A nitrile-stabilized carbanion is also involved in a synthesis of a fused pyranone system (81S225). A range of 2-ureidomethylenecyclohexane-l,3-diones, e.g. (308), react with activated acetonitriles in the presence of a strongly basic catalyst to produce 5-oxo-5,6,7,8-tetrahydrocoumarins (309). Since the substrates are readily available from cyclohexane-1,3-diones by reaction with triethyl orthoformate and a urea, the synthesis is attractive (Scheme 88). Furthermore, it has been applied to a pyran-2,4-dione, whereupon the 2,5-dioxopyrano[4,3-6]pyran (310) is formed. 

Activated nitro and halo substituents have been efficiently replaced by a variety of alkyl groups via SsAx reaction with carbanions. Examples include the displacement of the nitro group in compounds (10 X = 4-PhCO, 4-MeOCO, 4-CN, 4-N02, 4-PhS02, 3,5-(CF3>2) by the anion of 2-nitropropane in HMPA at room temperature (equation 2),83 and the reaction of p-dinitrobenzene with several ketones, esters and nitriles (RH equation 3) in Bu OK/liquid NH3 at -70 C.84 Interestingly, under the latter reaction conditions, p-chloronitrobenzene gave the product of alkylation rather than of SNAr displacement of chloride, as in equation (4).85 Further examples include the dehalogenation of p-halonitrobenzenes by 9-fluorenyl anions in DMSO at room temperature,34 and dehalogenation and denitration reactions by the carbanions of phenyl- and diphenyl-acetonitrile in DMSO or under PTC conditions.86... 

Quantum yields of photoinitiated reactions have been used as a qualitative measure of the chain length. The quantum yields for substitution of haloarenes with nitrile-stabilized carbanions range from 7 to 31 in liquid ammonia [24]. Quantum yields from 20 to 50 have been determined for the substitution of iodobenzene by (EtO)2PO ions [25]. 

Carbanions from hydrocarbons, nitriles, ketones, esters, TV./V-dialkyl acetamides and thioamides, and mono and dianions from (3-dicarbonyl compounds are some of the most common nucleophiles through which a new C-C bond can be formed. This C-C bond formation is also achieved by reaction with aromatic alkoxides. Among the nitrogen nucleophiles known to react are amide ions to form anilines however, the anions from aromatic amines, pyrroles, diazoles and triazoles, react with aromatic substrates to afford C-arylation. 

The main feature of carbanions derived from nitriles lies in the dependence on the aromatic substrate involved thus, two different outcomes of the substitution reaction are possible formation of the substitution compound by ET to the substrate from the radical anion intermediate 7, formed by coupling of phenyl radicals and acetonitrile anion, or formation of products from elimination of the cyano group as is the case with phenyl halides [31,32] (Sch. 3). The same reactivity pattern is found with halothiophenes [33]. 

Styryl carbanions readily react with carbon dioxide 31) to yield carboxy end groups. These terminal groups are also introduced by reaction with anhydrides 19) whereas the use of oxirane 23) leads to the formation of hydroxy end groups esters and nitriles are used to introduce carbonyl functions at the chain end. These reactions can be carried out at low temperature in THF solution and proceed quantitatively if no deactivation by protons occurs. 

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