Substitution nucleophile oxidation

Bartoli recently discovered that by switching from azide to p-anisidine as nucleophile, the ARO of racemic trans- 3-substituted styrene oxides could be catalyzed by the (salen)Cr-Cl complex 2 with complete regioselectivity and moderate selectivity factors (Scheme 7.36) [14]. The ability to access anti-P-amino alcohols nicely complements the existing methods for the preparation of syn-aryl isoserines and related compounds [67] by asymmetric oxidation of trans-cinnamate derivatives [68]. 

Allylic CH bonds Aliphatic alkenes frequently undergo allylic substitution by oxidation of the double bond to a radical cation that undergoes deprotonation at the allylic position and subsequent oxidation of the resulting allyl radical to a cation, which finally combines with the nucleophiles from the electrolyte [21, 22]. The selectivity is mostly low. Regioselec-tive allylic substitution or dehydrogenation is, however, found in some cases with activated alkenes, for example, -ionone that reacts to (1) (Fig. 5) as a major product [23], menthone enolacetate that yields 90% (2) [24], and 3,7-dimethyl-6-octen-l-ol... 

A great deal of work has been carried out on the thianthrene radical ion(l+), which can be produced from thianthrene by a variety of one-electron oxidations. The radical cation reacts at sulfur with nucleophilic species, giving rise to 5-substituted products, oxides, ylids, and 5-R-thianthrenium salts. 

Compared with the variety of existing carbon or nitrogen nucleophiles that were subjected to nucleophilic addition to there are few examples for phosphorus nucleophiles. Neutral trialkylphosphines turn out to be to less reactive for an effective addihon to Cjq even at elevated temperatures [114], Trialkylphosphine oxides show an increased reactivity. They form stable fullerene-substituted phosphine oxides [115] it is not yet clear if the reaction proceeds via a nucleophilic mechanism or a cycloaddition mechanism. Phosphine oxide addition takes place in refluxing toluene [115], At room temperature the charge-transfer complexes of with phosphine oxides such as tri-n-octylphosphine oxide or tri-n-butylphosphine oxide are verifiable and stable in soluhon [116],... 

There are several pathways by which one ligand may replace another in a square planar complex, including nucleophilic substitution, electrophilic substitution, and oxidative addition followed by reductive elimination. The first two of these are probably familiar from courses in organic chemistry. Oxidative addition and reductive elimination reactions will be covered in detail in Chapter 15. All three of these classes have been effectively illustrated by Cross for reactions of PtMeCItPMe-Ph),.-... 

Selectivity can be an overriding commodity in cases where reactivity is dictated by logic and accepted concepts. Such is the case with stannylene acetals of diols and trialkyl-stannyl ethers of alcohols. Enhanced nucleophilicity of oxygen attached to tin and well-documented stereoelectrorric effects associated with methine carbon atoms of trialkyhin ethers lead to remarkably selective reactions of (7-substitution and oxidation in polyhydroxy compounds. 

Substituted imidazole 1-oxides 228 are predicted to be activated toward electrophilic aromatic substitution, nucleophilic aromatic substitution, and metallation as described in Section 1. Nevertheless little information about the reactivity of imidazole 1-oxides in these processes exists. The reason for this lack may be the high polarity of the imidazole 1-oxides, which makes it difficult to find suitable reaction solvents. Another obstacle is that no method for complete drying of imidazole 1-oxides exists and dry starting material is instrumental for successful metallation. Well documented and useful is the reaction of imidazole 1-oxide 228 with alkylation and acylation reagents, their function as 1,3-dipoles in cycloadditions, and their palladium-catalyzed direct arylation. 

Other benzylic electrophiles which can lead to unexpected products are 1,2- or l,4-bis(halomethyl)benzenes. On treatment with a nucleophile, oxidation of the nucleophile instead of nucleophilic substitution may occur, followed by the formation of highly reactive quinodimethanes, which can either oligomerize or undergo addition or cycloaddition reactions (Scheme 4.29). The outcome of these reactions can, however, be controlled by choosing the right conditions, as demonstrated by the numerous report of successful Sn2 reactions at 1,2- or l,4-bis(halomethyl)benzenes (see, e.g., Ref. [125]). 

Increasingly sophisticated catalytic domains have been synthesized and used as adducts to the framework polymers. These synthetic macromolecules show substantially enhanced catalytic effects on hydrolytic reactions, decarboxylation, Schiffbase hydrolysis, aromatic nucleophilic substitution, and oxidation [63-69]. Several of these synthetic polymers are effective peptidases and nucleases. 

The sulfide-based linker 1.32 (89), obtained from commercial thio-PEG-PS resin and chloropyrimidine, is activated to nucleophilic substitution via oxidation with perbenzoic acid after multistep SP transformations treatment with amines then releases pure 2-aminopyrimidines in solution. Other nucleophiles should be suitable for the modular release of this and other heterocyclic S-supported nuclei. 

In general, the anodic oxidation of simple alkenes in nucleophilic solvents yields products resulting from both allylic substitution and oxidative addition of nucleophiles. Cyclohexene has been studied extensively as starting compound. The anodic oxidation of cyclohexene in methanol or acetic acid... 

There are two possible types of mechanism for the uncatalyzed hydrolysis of epoxides, a simple SN2 reaction of the substrate with water and a reaction of the protonated substrate with hydroxide ion. Another question to be answered concerns the position of attack of the nucleophile in substituted ethylene oxides. Experiments by Long and Pritchard [150] with H2180 indicate that in the uncatalyzed hydrolysis of propylene oxide two-thirds of the overall reaction occur via attack at the primary carbon. The corresponding percentage for the reaction of isobutylene oxide has not been determined precisely, but it is 20 % at least, probably much more. Attack at the primary carbon predominates also in the uncatalyzed reaction of propylene oxide with chloride ion [152]. 

Examples of relevant chemical transformation processes in aqueous environment are hydrolysis, nucleophilic substitution, elimination, oxidation and reduction reactions (Schwarzenbach et al, 1993). Of these, hydrolysis is often considered the most important and it is the only chemical transformation process for which international test guidelines are generally available. The tests for abiotic degradation of chemicals are generally in the form of determination of transformation rates under standardized conditions. 

Intramolecular nucleophilic attack of an amine group on an arene oxide has been proposed to account for the biosynthesis of a range of epipolythiopiperazine-diones (e.g., gliotoxin, bis-dithiobis-(methylthio)dehydrogliotoxin, spirodesmins, etc.)- With the amine-substituted arene oxides 50 and 55 (Figure 3), synthe-... 

Thus we see thai what at first appears to be a complicated reaction i actually a sequence of simple steps involving familiar, fundamental types of reactions acid-catalyzed dehydration, nucleophilic addition to an ,jS-unsaturaled carbonyl compound, electrophilic aromatic substitution, and oxidation. 

---