Nucleophilic attack stability

The Claisen condensation is initiated by deprotonation of an ester molecule by sodium ethanolate to give a carbanion that is stabilized, mostly by resonance, as an enolate. This carbanion makes a nucleophilic attack at the partially positively charged carbon atom of the e.ster group, leading to the formation of a C-C bond and the elimination ofan ethanolate ion, This Claisen condensation only proceeds in strongly basic conditions with a pH of about 14. 

Electron release from nitrogen stabilizes the carbonyl group of amides and decreases the rate at which nucleophiles attack the carbonyl carbon... 

The amide is activated toward nucleophilic attack by protonation of its carbonyl oxygen The cation produced m this step is stabilized by resonance involving the nitro gen lone pair and is more stable than the intermediate m which the amide nitrogen is protonated... 

The high chemical stability of pterins towards aqueous base is due to anion formation suppressing nucleophilic attack at a ring carbon atom by electrostatic repulsion. Substitution... 

Onium ions of small and large heterocyclics are usually produced by electrophilic attack on a heteroatom. In three- and four-membered rings nucleophilic attack on an adjacent carbon follows immediately, in most cases, and ring opening stabilizes the molecule. In large rings the onium ion behaves as would its acyclic analog, except where aromaticity or transannular reactions come into play (each with its electronic and steric pre-conditions). A wide diversity of reactions is observed. 

Azetidine, 7V-bromo-, 7, 240 Azetidine, AT-r-butyl- N NMR, 7, 11 Azetidine, AT-t-butyl-3-chloro-transannular nucleophilic attack, 7, 25 Azetidine, 3-chloro-isomerization, 7, 42 Azetidine, AT-chloro-, 7, 240 dehydrohalogenation, 7, 275 Azetidine, 7V-chloro-2-methyl-inversion, 7, 7 Azetidine, 3-halo-synthesis, 7, 246 Azetidine, AT-halo-synthesis, 7, 246 Azetidine, AT-hydroxy-synthesis, 7, 271 Azetidine, 2-imino-stability, 7, 256 Azetidine, 2-methoxy-synthesis, 7, 246 Azetidine, 2-methyl-circular dichroism, 7, 239 optical rotatory dispersion, 7, 239 Azetidine, AT-nitroso-deoxygenation, 7, 241 oxidation, 7, 240 synthesis, 7, 246 Azetidine, thioacyl-ring expansion, 7, 241 Azetidine-4-carboxylic acid, 2-oxo-oxidative decarboxylation, 7, 251 Azetidine-2-carboxylic acids absolute configuration, 7, 239 azetidin-2-ones from, 7, 263 synthesis, 7, 246... 

The orientation of nucleophilic attack on a fluoroolefin is influenced also by the presence on the fluoroolefin of electron-withdrawing functional groups that stabilize the intermediate carbanion. Thus nucleophilic attack tends to be oriented... 

Notwithstanding the expected and also observed high reactivity of the intermediate immonium ions, the stabilization of the exocyclic double bond in the pyrrolidino derivative evidently prevents rapid nucleophilic attack of water and the hydration of this ion to the amino alcohol becomes a slow general base-catalyzed process in weakly acidic solutions [Eq. (6)]. 

Ortho esters are one of the few derivatives that can be prepared from acids and esters that protect the carbonyl against nucleophilic attack by hydroxide or other strong nucleophiles such as Grignard reagents. In general, ortho esters are difficult to prepare directly from acids and are therefore more often prepared from the nitrile. Simple ortho esters derived from normal alcohols are the least stable in terms of acid stability and stability toward Grignard reagents, but as the ortho ester becomes more constrained, its stability increases. 

For trisubstituted olefins, the nucleophile attacks predominantly at the less substituted end of the allyl moiety, e.g. to afford a 78 22 mixture of 13 and 14 (equation 7). Both the oxidative addition of palladium(O) and the subsequent nucleophilic attack occur with inversion of configuration to give the product of net retention7. The synthesis of the sex pheromone 15 of the Monarch butterfly has been accomplished by using bis[bis(l,2-diphenylphosphinoethane)]palladium as a catalyst as outlined in equation 87. A substitution of an allyl sulfone 16 by a stabilized carbon nucleophile, such as an alkynyl or vinyl system, proceeds regioselectively in the presence of a Lewis acid (equation 9)8. The... 

Sulfur-stabilized ylides underwent photodriven reaction with chromium alkoxy-carbenes to produce 2-acyl vinyl ethers as E/Z mixtures with the E isomer predominating (Table 22) [ 121-123]. The reaction is thought to proceed by nucleophilic attack of the ylide carbon at the chromium carbene carbon followed by elimination of (CO)5CrSMe2. The same reaction occurred thermally, but at a reduced rate. Sulfilimines underwent a similar addition/elimination process to produce imidates or their hydrolysis products (Table 23) [ 124,125]. Again the reaction also proceeded thermally but much more slowly. Less basic sulfilimines having acyl or sulfonyl groups on nitrogen failed to react. 

The electrophilicity and therefore the stability of the cationic chain ends are relatively limited, because, on the one hand, the electrophilicity must be large enough to aid a nucleophilic attack by the monomer, but on the other hand, not so large that a chain termination occurs due to recombination with the counterion. For this reason the stability of the cationic chain ends is a function of ... 

Head-to-head [2+2]photocycloaddition of 1,2-diarylethanediones and 2-aminopropene nitriles (CH2 C(CN)NR2) occurs to yield oxetanes 10 in moderate to good yields. The formation of only one diastereoisomer in each of the cases investigated is rationalized in terms of the most easily accessible and stabilized 1,4-diradical intermediate <95RTC498>. 2,3,4-Trisubstituted oxetanes 11 are obtained in high yield by intramolecular nucleophilic attack of the anion from certain 2-(l-alkoxyethyl)-3-substituted oxiranes <96JOC4466>. 

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

In these a-phosphorylated dithioesters, the electron-withdrawing effect of the phosphono group, which strongly increases the electrophilic character of the thiocarbonyl group, makes the latter more prone to the thiophilic attack of nucleophiles and stabilizes the resulting carbanion. The main reactions of 1 with nucleophiles are summarized in Scheme 2. 

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