Addition of electrophilic carbon

Additions of electrophilic carbon to cyanides are well known ". They occur in e.g. the Ritter reaction which has been reviewed extensively by BishopIn this reaction a carbenium ion, generated from e.g. r-butanol and sulphuric acid, attacks the nitrogen atom of a cyanide (equation 36). Sometimes, cyanides are applied to trap carbocations. An ex-... 

More important than proton additions are additions of electrophilic carbon by which a new carbon-carbon bond is formed. Carbon-carbon bond formation is a major goal in the synthesis of organic compounds. For instance, from a carboxylic acid chloride an a-oxoimidoyl chloride (70) is prepared Addition of a carbocation to an isocyanide gives a species that is identical to the ion obtained in the Ritter reaction " cf. Section III. 

The Johnson group began by examing the solvolysis of 5-hexenyl nosylate (65) in formic acid. This reaction gave only small amounts of cyclohexanol and cyclohexene, but illustrated that that cyclization was possible. Solvolysis of diene 66 gave cyclohexanol 67 as the major product. This product results from addition of the electrophilic carbon (Ci) and oxygen nucleophile (formate) across the fm r-olefin. Decalins 68-70 were produced in low yields, but it was notable that only fm -fused decalins were produced. This observation was consistent with an addition of electrophilic carbon (Ci) and nucleophilic carbon (Cio) across the af-olefin (see B in Steroids-12). 

N-Acyliminium ions are hot and will even add to unactivated olefins. For example, N, 0-acetal 20 reacts with formic acid to provide 23. The stereochemistry of the process is relatively clean and can be rationalized by an twft -periplanar addition of electrophilic carbon and nucleophilic oxygen across the carbon-carbon double bond with a transition state that resembles a chair N-acylpiperidine. In reality, this process is mechanistically more complex than this simple model (for example, possible carbocation intermediates and in some cases, some underlying sigmatropic rearrangements), but the model is simple, easy to remember, and has excellent predictive value. How was this chemistry used to prepare perhydrohistrionicotoxin ... 

Additions of Electrophilic Carbon A new, FeCl3-catalysed ene-type reaction of propargylic alcohols (74) with 1,1-diaryl... 

Chemical Properties. The chemistry of ketenes is dominated by the strongly electrophilic j/)-hybridi2ed carbon atom and alow energy lowest unoccupied molecular orbital (LUMO). Therefore, ketenes are especially prone to nucleophilic attack at Cl and to [2 + 2] cycloadditions. Less frequent reactions are the so-called ketene iasertion, a special case of addition to substances with strongly polarized or polarizable single bonds (37), and the addition of electrophiles at C2. For a review of addition reactions of ketenes see Reference 8. 

Absolute rate constants for the attack of aryl radicals on a variety of substrates have been reported by Scaiano and Stewart (Ph ) 7 and Citterio at al. (/j-CIPh-).379,384 The reactions are extremely facile in comparison with additions of other carbon-centered radicals [e.g. jfc(S) = 1.1x10s M"1 s"1 at 25 °C].3,7 Relative reactivities are available for a wider range of monomers and other substrates (Tabic 3.b). Phenyl radicals do not show clear cut electrophilic or... 

Benzotriazole-related methodology publications appeared in 2006. Reaction of 1-formylbenzotriazole with triphenylphosphine/carbon tetrachloride afforded l-(2,2-dichlorovinyl)benzotriazole, where lithiation followed addition of electrophiles gave a variety of functionalized M-(ethynyl)benzotriazoles <06T3794>. Novel mono- and symmetrical di-/V-hydroxy- and IV-aminoguanidines were readily prepared from the reaction of diverse hydroxylamines or hydrazines with reagent classes di(benzotriazol-l-yl)methanimine, (bis-benzotriazol-1 -y 1-methy lene)amines, benzotriazole-1 -carboxamidines, benzotriazole-1 -... 

Scheme 6.63 Addition of atomic carbon to pyrrole and N-methylpyrrole and interception of the zwitterions 179-Zn and 293-Z, by electrophiles, according to Shevlin and co-workers.

Cycloalkenones are ubiquitous as reactive intermediates and bioactive materials. Modification of a simple cycloalkenone by addition of a carbon substituent at the o-position should be a useful transformation, but one that is not readily accomplished by conventional enone chemistry. a-Substituted cycloalkenones could of themselves be of interest, but perhaps, of more general importance would be their use as intermediates for the production of substituted cycloalkanones or a, 5-disubstituted cycloalkanones by a subsequent conjugate addition procedure.2 These strategies avoid many of the limitations attendant to the trapping of enolates with carbon electrophiles. The method of Kim involving treatment of enones with the combination of a dimethyl acetal, pyridine and trimethylsilyl triflates results in a-(1-methoxyalkyljenones.3 The metallation of a-bromoenones masked as ketals for [Pg.184]

Addition of electrophilic mercury(II) salts to carbon-carbon double bonds in nucleophilic solvents (i.e. oxymercuration, solvomercuration etc.) is a well documented methodology in organic synthesis146. In these reactions a mercuric salt, usually the chloride or... 

The addition of electrophilic reagents to chiral a,/3-unsaturated sulfoxides is also accompanied by asymmetric induction. Stirling and Abbott (318,322) found that the addition of bromine to the optically active (.R)-vinyl-p-tolyl sulfoxide 319 yields a mixture of diastereo-meric a,/3-dibromosulfoxides 320. Oxidation of this mixture gives the optically active sulfone 321, with a center of chirality at the a-carbon atom only. The optical purity (32%) of this sulfone was estimated by comparing its specific rotation with that obtained as a result of oxidation of diastereomerically pure sulfoxide (/ )-320. The assignment of configuration at the a-carbon atom was based on the analysis of the polarizabilities of substituents. 

Electrophilic vinylidene complexes, capable of reacting with non-carbon nucleophiles to yield Fischer-type carbene complexes, can be obtained by addition of electrophiles to alkynyl complexes (Figure 2.11, Table 2.7, Entries 11, 12) [134,144]. 

Addition of Nucleophiles Addition of Electrophiles to Ring Carbon Addition of Electrophiles to Ring Nitrogen... 

To understand the reason for the pronounced selectivity in the orientation of addition of electrophiles, it will help to consider one example, hydrogen bromide addition to 2-methylpropene. Two different carbocation intermediates could be formed by attachment of a proton to one or the other of the doublebond carbons ... 

This transformation is of value because it makes an electrophilic carbon into a nucleophilic carbon. Organometallic compounds are a convenient source of nucleophilic carbon. A typical example of their utility is the way they achieve addition of nucleophilic carbon to carbonyl groups with formation of carbon-carbon bonds ... 

Carbocations with trivalent carbon may have carbon with coordination number 2. Acyl ions have already been mentioned the vinyl cations, or car-bynium ions (26), have been detected as intermediates in addition of electrophiles to acetylenes and allenes and in solvolysis reactions with the highly reactive trifluoromethanesulfonate (triflate) leaving group.84 Vinyl cations are expected... 

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