Nitrogen nucleophiles mechanisms

Preparing Aldehydes and Ketones A Review Introduction to Nucleophilic Addition Reactions Oxygen Nucleophiles Nitrogen Nucleophiles Mechanism Strategies Sulfur Nucleophiles Hydrogen Nucleophiles Carbon Nucleophiles Baeyer-Villiger Oxidation of Aldehydes and Ketones Synthesis Strategies... 

Kinetic data on acetate displacement from C-3 using a number of sulfur and nitrogen nucleophiles in aqueous solution at near neutral pH demonstrate that the reaction proceeds by an 5 1 mechanism (B-72MI51004). The intermediate in this reaction is depicted as a dipolar allylic carbonium ion (9) with significant charge delocalization. Of particular significance in this regard is the observation that the free carboxylate at C-4 is required since... 

All the mechanisms so far discussed take place at a saturated carbon atom. Nucleophilic substitution is also important at trigonal carbons, especially when the carbon is double bonded to an oxygen, a sulfur, or a nitrogen. Nucleophilic substitution at vinylic carbons is considered in the next section at aromatic carbons in Chapter 13. 

The addition-elimination mechanism has been used primarily for arylation of oxygen and nitrogen nucleophiles. There are not many successful examples of arylation of carbanions by this mechanism. A major limitation is the fact that aromatic nitro... 

Note that, in all of these reaction mechanisms, a proton needs to be removed from the nitrogen nucleophile. Hence ammonia, primary amines, and... 

V-Alkoxy-V-chloroureas (77) have also been reacted with nitrogen nucleophiles resulting in Sat2 displacement of chloride. The products suggest that the reaction proceeds via an unstable V-alkoxy-V-amino intermediate (78), which under the influence of hydrochloric acid formed in the reaction, decomposed as illustrated to diaminomethane (79) and urea (80) (Scheme 15), although the exact mechanism is unclear . 

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],... 

To minimize any ambiguity in interpretation, we have prepared modified polyethylenimines in which all the nitrogens have been quaternized, with various apolar groups, so that they cannot function in a nucleophilic mechanism. Some of the derivatives prepared may be represented by the stoichiometric formulas... 

The conversion of an amide in this way is termed the Hofmann reaction or the Hofmann rearrangement. The mechanism of the reaction involves an intramolecular 1,2-carbon-to-nitrogen nucleophilic shift of the alkyl (or aryl) group... 

Azasulfenylation of alkenesf s The adducts of dimethyl(methylthio)-sulfonium tetrafluoroborate (1) with alkenes react slowly but smoothly with various nitrogen nucleophiles to give products of overall rrarw-addition to the alkene. Regioselectivity depends on the substitution pattern of the alkene and on the nucleophilicity of the attacking reagent, and is subject to some control. The mechanism of this azasulfenylation is not certain it may involve an episulfonium ion. 

Tab. 9.2 Condensation Reactions of Nitrogen Nucleophiles with Carbonyl Compounds Through Which C=N Double Bonds are Established-Mechanism and Scope...

The most common method to decrease the reactivity of an unshared pair of electrons on an atom is to attach a carbonyl group to that atom. Therefore, the amine is first reacted with acetyl chloride to form an amide. (This reaction and its mechanism are described in detail in Section 19.6. To help you remember the reaction for now, note that the nitrogen nucleophile attacks the carbonyl carbon electrophile, displacing the chloride leaving group.)... 

Hydroamination of olefins is also possible with gold catalysts. In this reaction, the attack comes Ifom a nitrogen nucleophile as a carbamate,a urea, an amide, or a sulfonamide. In the latter case, the reaction can be carried out intermolecularly. While the carbamates, ureas, and amides give only products of intramolecular anunations, the sulfonamides can perform the intermolecular addition. Only the addition of ureas (equation 146) takes place at room temperature, and in the rest of the additions heating is required. The catalysts of choice in all these reactions are cationic gold(I)-species stabilized by phosphines or NHC ligands. The reaction times have been reduced by the use of microwave irradiation. The mechanism of the hydroamination reaction has been studied in detail theoretically. ... 

The cyclization of 4,5-hexadienamines and -amides, catalyzed by palladium salts in the presence of copper(II) chloride under a carbon monoxide atmosphere, afforded 2-(2-pyrrolidinyl)acrylates. A different mechanism is operating here, which does not involve the intramolecular addition of nitrogen nucleophile to a rt-complex, but, instead, the addition of PdX2 to a double bond, followed by SN2 or S 2 displacement in the cyclization step28. 

In addition to the most important 1,2-difunctionalization assisted or catalyzed by palladium(II) complexes, a catalytic 1,1-arylamination process of alkenes, applied to the construction of nitrogen heterocycles from 4-pentenylamides, was realized29,30. The mechanism involves the formation of arylpalladium chloride from alkyl(aryl)stannanes, the addition to the alkene, the isomerization of the adduct to the more stable benzylic palladium complex, and the displacement of palladium by an internal nitrogen nucleophile. In the presence of a substituent, mixtures of diastereomers were generally obtained. 

The identity of the nitrogen nucleophile determines the type of amine or ammonium salt formed as product. One new carbon-nitrogen bond is formed in each reaction. Because the reaction follows an Sn2 mechanism, the alkyl halide must be unhindered—that is, CH3X or RCH2X. 

Cyano-derivatives can be readily obtained by a ruthenium-catalyzed addition of various hydrazines to terminal alkynes [89] in which the cyano carbon atom arises from the terminal alkyne carbon atom. The tris(pyrazolyl)borate (Tp) complex RuCl(Tp)(PPh3)2 (1 mol%) was found to be the most active catalyst, and N,N-dimethylhydrazine (5 equiv.) the best nitrogen source. The proposed mechanism involves the nucleophilic attack of the nitrogen nucleophile on the a-carbon of a vinylidene intermediate (Scheme 8.27). Proton migration in the resulting a-hydrazi-nocarbene, followed by deamination, would give the nitrile derivative and regenerate the catalytic species. 

The other nitrogen nucleophile available to enzymes is the versatile imidazole ring of histidine. This group is used more often for acid/base chemistry, but it is used occasionally as a nucleophile in, for example, phosphotransfer reactions. The serine proteases, such as a-chymotrypsin, which is illustrated in Figs. 2a and (2)b, are classic examples of the participation of serine as a nucleophile. Additional examples exist of nucleophilic mechanisms that employ the hydroxyl groups of threonine and tyrosine and the carboxylate groups of aspartate and glutamate. 

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