Nucleophilic reactions conversion

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

Benzodiazepines as antianxiety agents, 1, 170 as anticonvulsants, 1, 166 organometallic complexes, 7, 604 as sedatives, 1, 166 IH- 1,2-Benzodiazepines conversion to 3H-1,2-benzodiazepines, 7, 604 synthesis, 7, 597, 598, 604 3H-1,2-Benzodiazepines acid-catalyzed reactions, 7, 601 nucleophilic reactions, 7, 604 oxidation, 7, 603 synthesis, 7, 596 thermal reactions, 7, 600 5H-1,2-Benzodiazepines photochemical reactions, 7, 599 synthesis, 7, 603... 

Some of the most important evidence for the two-step mechanism comes from studies of base catalysis, in this regard, reactions involving primary and secondary amines have played a central role1-5. The initially formed cx-adduct, 1, is zwitterionic and contains an acidic proton, which can be removed by a base which may be the nucleophile itself. Conversion of 1 to products can then occur via the uncatalysed k2 pathway or via the base-catalysed hl pathway. The influence of Brpnsted base catalysis, the experimental observation of 1,1- and 1,3-cr-adducts, the sensitivity of the system to medium effects, are some experimental evidence of the mechanism depicted in equation 1. 

Indeed, the application of less nucleophilic solvent than methanol (e.g., trifluor-oethanol) was found to be successful for the improvement of the reaction conversion level and helped to prevent the side-reactions. 

The alkylation of quinoline by decanoyl peroxide in acetic acid has been studied kineti-cally, and a radical chain mechanism has been proposed (Scheme 207) (72T2415). Decomposition of decanoyl peroxide yields a nonyl radical (and carbon dioxide) that attacks the quinolinium ion. Quinolinium is activated (compared with quinoline) towards attack by the nonyl radical, which has nucleophilic character. Conversely, the protonated centre has an unfavorable effect upon the propagation step, but this might be reduced by the equilibrium shown in equation (167). A kinetic study revealed that the reaction is subject to crosstermination (equation 168). The increase in the rate of decomposition of benzoyl peroxide in the phenylation of the quinolinium ion compared with quinoline is much less than for alkylation. This observation is consistent with the phenyl having less nucleophilic character than the nonyl radical, and so it is less selective. Rearomatization of the cr-complex formed by radicals generated from sources other than peroxides may take place by oxidation by metals, disproportionation, induced decomposition or hydrogen abstraction by radical intermediates. When oxidation is difficult, dimerization can take place (equation 169). 

It is well established that the nucleophilic reaction of alkoxides with 3-chlorobicyclo[1.1.0]butane-1-carbonitrile leads to 3,3-dialkoxycyclobutane-1-carbonitriles.31 The mechanism of this conversion is shown. 

Notes Ligand. Used for Pd-catalyzed nucleophilic reactions at allylic positions. See also, Dodd. With Br forms a useful brominating agent, l,2-bis(diphenylphosphino)ethane tetrabromide [7726-95-6],1 This reagent is useful for the conversion ... 

Radicals are often classified according to their rates of reactions with alkenes. Those radicals that react more rapidly with electron poor alkenes than with electron rich are termed nucleophilic radicals. Conversely, those that react more rapidly with electron rich alkenes than electron poor are termed electrophilic radicals. Recently, it has been found that this simple division does not suffice because certain radicals react more rapidly with both electron rich and electron poor alkenes than they do with alkenes of intermediate electron density. These radicals are termed ambiphilic. The appropriate pairing of a radical and an acceptor is important for the success of an addition reaction. 

In the course of the reaction, the nitrite ion leaves the primary anion radical. This produces the cyclohexyl radical in a pyramidal configuration. The vicinal methyl group steri-cally hinders the conversion of the pyramidal radical into the planar one. With a high concentration of the nucleophile, the rate of addition exceeds the rate of conversion i.e. radd > rconv Then the entering PhS group occupies the axial position. With a low concentration of the nucleophile, the conversion occurs earlier than the addition (radd rconv) and the planar radical center is attacked from both the axial and equatorial sides. This results in the formation of the isomer mixture. 

An electrophile is often likely to attack a position that has more electron density in the HOMO. This is because the electrons in the HOMO are more accessible and more polarizable than are the electrons in the lower energy MOs. Conversely, in the case of a nucleophilic reaction, the attacking agent often prefers to go where the LUMO offers a large, accessible lobe with which the orbitals of the nucleophile can overlap and interact. 

A similar distinction between a system with pre-electrolysis with only one electrode (in this case anodic) process, and a system with simultaneous anodic and cathodic processes (in which anode and cathode are on opposite walls of a microchannel so that each liquid is only in contact with the desired electrode potential, analogous to the fuel cell configurations discussed above) was made by Horii et al. (2008) in their work on the in situ generation of carbocations for nucleophilic reactions. The carbocation is formed at the anode, and the reaction with the nucleophile is either downstream (in the pre-electrolysis case) or after diffusion across the liquid-liquid interface (in the case with both electrodes present at opposite walls). The concept was used for the anodic substitution of cyclic carbamates with allyltrimethylsilane, with moderate to good conversion yields without the need for low-temperature conditions. The advantages of the approach as claimed by the authors are efficient nucleophilic reactions in a single-pass operation, selective oxidation of substrates without oxidation of nucleophile, stabilization of cationic intermediates at ambient temperatures, by the use of ionic liquids as reaction media, and effective trapping of unstable cationic intermediates with a nucleophile. 

Conversely, the decrease in the rate constant for the hydroxide ion catalyzed reaction of l,l,l-trichloro-2-methyl-2-propanol in the presence of polyoxyethylene(23) dodecanol and polyoxyethylene sorbitan mono-decanoate has been rationalized by assuming that the nucleophilic reaction occurs only in the bulk solution and that a substantial fraction of the substrate is solubilized by the surfactant. The latter assumption was verified by measurements of the solubility of l,l,l-trichloro-2-methyl-2-propanol, and hence the distribution coefficients, in the micellar systems (Anderson and Slade, 1966). 

Nucleophilic reactions of unmodified aldehydes are usually diiScult to control, affording complex mixture of products, often due to the high reactivity of the formyl group under either basic or acidic reaction conditions. The activity order of the supported amines was secondary > primary > tertiary, which may suggest the intervention of an enamine pathway the enals were exclusively obtained as ( ) isomers. Notably, FSM-16-(CH2)3-NHMe exhibited higher activity than conventional solid bases such as MgO and Mg-Al-hydrotalcite [hexanal self-aldol condensation FSM-16-(CH2)3-NHMe 97% conversion and 85% yield in 2h, MgO 56% conversion and 26% yield in 20 h, Mg-Al-hydrotalcite 22% conversion and 11% yield in 24 h]. 

The chemical reactivity of simple heterocyclic aromatic compounds varies widely in electrophilic substitution reactions, thiophene is similar to benzene and pyridine is less reactive than benzene, while furan and pyrrole are susceptible to polymerization reactions conversely, pyridine is more readily susceptible than benzene to attack by nucleophilic reagents. These differences are to a considerable extent reflected in the susceptibility of these compounds and their benzo analogues to microbial degradation. In contrast to the almost universal dioxygenation reaction used for the bacterial degradation of aromatic hydrocarbons, two broad mechanisms operate for heterocyclic aromatic compounds ... 

---