Alkylation electrophilic

This realization led me to study related possible intermolecular electrophilic reactions of saturated hydrocarbons, Not only protolytic reactions but also a broad scope of reactions with varied electrophiles (alkylation, formylation, nitration, halogenation, oxygenation, etc.) were found to be feasible when using snperacidic, low-nucleophilicity reaction conditions. 

Such methyenepyrans afford still another possibility for obtaining new pyrylium salts, namely, electrophilic alkylation or acylation at the exocyclio methylene carbon atom. Thus, 2,6-diphenyl-4-iso-propylidene-4/I-pyran is converted into 2,6-diphenyl-4-i-butyl-pyrylium iodide on refluxing with methyl iodide (see Scheme 3). Unlike the protonation of methylenepyrans, this reaction is no longer... 

Another method for the synthesis of epoxides is through the use of halo-hydrins, prepared by electrophilic addition of HO—X to alkenes (Section 7.3). When halohydrins are treated with base, HX is eliminated and an epoxide is produced by an intramolecular Williamson ether synthesis. That is, the nucleophilic alkoxide ion and the electrophilic alkyl halide are in the same molecule. 

Perhaps the single most important reaction of enolate ions is their alkylation by treatment with an alkyl halide or tosylate, thereby forming a new C-C bond and joining two smaller pieces into one larger molecule. Alkylation occurs when the nucleophilic enolate ion reacts with the electrophilic alkyl halide in an SN2 reaction and displaces the leaving group by backside attack. 

Unlike regular aziridine-2-carboxylic esters, aziridine-2-carboxylic thioester 174 (Scheme 3.62) forms stable carbanions at the 2-position upon treatment with base [13b, 122]. Thus, electrophilic alkylations of aziridine 174 afforded products 175. The reactions were highly diastereoselective, affording 175 in moderate to good... 

Rutavicius and Kuodis reported several examples of electrophilic alkylations of the ring nitrogen atom in 5-(4-pyridyl)-l,3,4-oxadiazol-2-thiones (Scheme 7) sometimes, the reaction on nitrogen was accompanied by alkylation on sulfur atom. The direction of substitution depended both on the structure of the initial reactants and on the reaction conditions <2002CHE852>. 

Meyers lactams are widely used in synthesis of substituted synthons of interest and their functionalization is carried out under strong base conditions giving C-alkyl derivatives. Alkylation of bicyclic lactam 182 with electrophiles (alkyl, allyl, benzyl halides, chlorophosphonate), and a strong base (j-BuLi, LiHMDS, or KHMDS HMDS = hexamethyldisilazide) in THF at — 78 °C gave an endo-exo mixture of products where the major one is the rro/o-compound 183 in good yields. The ratios were determined by H NMR spectroscopy and are usually up to... 

Stannyllithium compounds are important as sources of nucleophilic stannyl anions, and the dialkyltin lithium hydrides, R2SnLiH, have recently come to prominence as their reaction with electrophilic alkyl halides gives hydrides, R1R2SnH, with mixed alkyl groups (see Section 3.14.18.1).397... 

While the formation of multiadducts in the above reactions clearly demonstrates the difficulties confronted in terms of controlling the reaction, the issue of whether C6o and C70 undergo addition by carbon electrophiles is of great interest, because such a reaction would provide a useful method for carbon-carbon bond formation for the derivatization of fiillerenes. Initial attempts to test the possibility of electrophilic alkylation of C6o with terf-butyl chloride and AICI3 gave only polymeric products, probably formed via isobutene, indicating the insufficient reactivity of C60 towards terf-butyl cation. 

When imines are the nucleophiles used, the initially formed iminium intermediates can undergo intramolecular electrophilic alkylation of the other ligands (e.g. Entry 2, Table 2.10 see also [143]). In addition to this, carbyne complexes can also react with azides to give metallatriazoles [185,186] (Entry 6, Table 2.10). 

The 1,6-addition reaction of lithium amides to the naphthalene ring system (141) followed by the electrophilic alkylation has been reported (Scheme 17). ... 

In addition to the electrophilic alkylation, the phosphinyl-benzophospho-lide 25 reacted also with sulphur, BH3-thf, and trimethylsilyl azide under selective conversion of the Ph2P-moiety to give the corresponding thioxophos-phorane, borane-adduct, and iminophosphorane, respectively [33, 37], and quaternisation with chloro-acetonitrile followed by deprotonation gave access to a zwitterionic phosphonio-benzophosphohde with an exocyclic ylide-substituent [37]. 

Plant sterols such as stigmasterol typically contain an extra ethyl group when compared with cholesterol. Now this is not introduced by an electrophilic ethylation process instead, two successive electrophilic methylation processes occur, both involving SAM as methyl donor. Indeed, it is a methylene derivative like that just seen in ergosterol formation that can act as the alkene for further electrophilic alkylation. After proton loss, the product has a side-chain with an ethylidene substituent the side-chains of the common plant sterols stigmasterol and sitosterol are then related by repeats of the reduction and dehydrogenation processes already seen in ergosterol formation. 

Tertiary electrophiles alkylate bydroxylamines through the SatI mechanism. These reactions (e.g. equation 10) are practically feasible only for compounds forming highly stabilized carbocations such as trityl , or 2-(p-alkoxyphenyl)propyl. All these reactions proceed exclusively on the nitrogen atom and have been used for A-protection of the amino groups in bydroxylamines. 

Alkylation of 5-amino-1,2,4-thiadiazoles (17) with methyl iodide leads to N-4 derivatives of type (18) which undergo a Dimroth rearrangement to (110) on warming in ethanol when R = H (Scheme 26). When R = methyl, phenyl, or benzyl the reaction is severly hindered <84CHEC-I(6)463>. In contrast, benzhydryl and trityl chlorides (which are harder electrophiles) alkylate (17) at the 5-amino function to give compounds of type (109) (Scheme 26). 

Direct electrophilic alkylation in the pyrimidine 5-position can be carried out on pyrimidines with at least two strongly donating groups, more readily with three such groups. For example, uracil can be 5-hydroxymethylated by formaldehyde under alkaline conditions, and a microwave-assisted procedure has now been developed which allows formation of 5-hydroxymethyluracil in 98% yield, with just 3 min of reaction time <2002SL2043>. 

Hydrolytic reactions can also be applied in the synthesis of aldehydes or ketones via the corresponding 1,3-oxazine derivatives. The anion formed from 3-methyl-2-(4-pyridyl)tetrahydro-l,3-oxazine 155 on treatment with BuLi proved to react with various electrophiles (alkyl halides, carboxylic esters, acid chlorides, or aldehydes) exclusively at position 2 of the 1,3-oxazine ring and not at the pyridine nitrogen atom. The readily formed 2,2-disubstituted-l,3-oxazine... 

The very unstable hydroxy nitrosamine then loses formaldehyde to form the primary alkynitrosamine, which rapidly rearranges to the alkyl diazonium ion. The latter, being a powerful electrophile, alkylates various cellular nucleophiles, including the nucleic acids. 

Isopropylation over HY, HL and Other Zeolites - The catalysis over HY and HL zeolites is quite different from that over HM. The product distribution over HY and HL resembled that of SA the formation of 4,4 -DIPB was non-regioselective (Table l).18-1 These catalyses are not controlled by the environments of the pores because both zeolites have sufficiently large pores for the transition states form all the IPBP and DIPB isomers. Instead, the product distribution markedly changes by the reaction temperature. At low temperatures, the products are determined by the reactivity at 2- and 4-positions of biphenyl for electrophilic alkylation to yield principally 2- and 4-IPBP for IPBP isomers and... 

Substituted cyclobutenes 2-substituted 1,3-dienes. The reagent reacts with various electrophiles (alkyl halides, carbonyl compounds, epoxides) to give the corresponding selenides, jS-hydroxy- and y-hydroxyselenides, respectively. Three methods can be used to convert these adducts to cyclobutenes, as shown in equations... 

Alkylation with Alcohols. Alkylation of aromatic hydrocarbons with alcohols86 151153 in the presence of protic catalysts yields the products expected from typical electrophilic alkylation ... 

Since numerous monographs and review papers cover in detail nearly all aspects of electrophilic aromatic substitutions, only a brief overview of some important reactions resulting in heterosubstitution is given here. Electrophilic alkylation of aromatics, the most important electrophilic substitution with regard to hydrocarbon chemistry, including new C—C bond formation, in turn, is discussed in Section 5.1.4. 

Oxathiolane 3,3-dioxide (332) metallates in its 2-position to yield an anion which reacts with various electrophiles (alkyl halides and carbonyl compounds) to give substituted oxathiolanes (333) in good to excellent yield (79TL3375). Pyrolysis of these alkylated products affords the corresponding aldehydes or 2-hydroxyaldehydes in addition to sulfur dioxide and isobutylene (Scheme 71). The oxathiolane (332) thus becomes another member of the already burgeoning class of carbonyl anion equivalents. 

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