Nucleophile carbon-containing

Analogous displacements have been carried out with thioalkoxide and thiophenoxide ions. Chloride ion has also been displaced from 2-chloro-quinoxalines with various carbon-containing nucleophiles derived from active methylene compounds. For example, with benzyl cyanide, the substituted acetonitrile 9 is obtained and with the carbanions derived from ketones, 2-quinoxalinylketones of type 10 are produced. ... 

Haloalkanes also react with carbon nucleophiles. These reactions increase the length of the carbon chain. One example of a carbon-containing nucleophile is cyanide ion (CN), which reacts with haloalkanes to give nitriles with the formula R—CN. We will see later that nitriles can be transformed into carboxylic acids and amines. Carbon-containing nucleophiles derived from aUtynes are called alkynide ions. These nucleophiles, the conjugate bases of alkynes, react to form alkynes containing the carbon atoms of both the haloalkane and the alkynide. 

It is very likely, that this reaction occurs due to the equilibrium between trimethylsilyl halide and a nitrogen-containing nucleophile, which increases the electrophilicity of silyl Lewis acids. It should be noted that the configuration of stereocenters at the carbon atoms of the oxazine ring is partially distorted. Hence, it is assumed that the reaction proceeds through the intermediate cation B, which is partially isomerized into the stereoisomeric cation B through the open chain cation B". 

Alkylideneallyl cations can be described as resonance hybrids of 1-vinyl-substituted vinyl cations and allenylmethyl cations, and thus contain two reactive sites (the sp- and sp2-hybridized carbons) for nucleophilic addition (Scheme 1) (7,2). Hybridization affects the electronic and steric character of these reaction sites. The electronic property was deduced from the l3C NMR chemical shifts of alkylideneallyl cations measured under superacidic conditions (3) and also from the charge distribution calculated (4). The charge distributions are affected by substituents on the cation the sp2 carbon is more positive than the sp carbon when two methyl groups are introduced at the sp2 carbon. 

In addition, unstabilized enolate nucleophiles have been generated by decarboxylation of (3-ketocarboxylates. In this case, no additives are required to activate the nucleophile, but the highest yields and selectivities were obtained in the presence of two equivalents of DBU [82]. Although reactions of allylic carbonates containing aromatic, heteroaromatic, and aliphatic substituents occurred, only reactions to form aryl ketone products were published. 

Carbon disulfide, thiourea, and related reagents. Culvenor and co-workera888 387 have examined the action on ethylene oxides of several interesting sulfur-containing nucleophiles in addition to those already considered. 

Carbon-centered nucleophiles are those compounds or intermediates which contain an electron-rich carbon atom and thus are capable of donating an electron pah from that carbon atom to an electrophile. The electron pair that is donated is found in a filled orbital in the nucleophilic carbon and the electrons are not tighdy bound. Donation to the electrophilic carbon occurs by overlap of the filled orbital of the donor with an unfilled orbital of the acceptor. The most common carbon nucleophiles fall into three main classes ... 

A review of the metal-catalysed ring opening of achiral epoxides by achiral carbon-, sulfur-, nitrogen- and halogen-containing nucleophiles and kinetic resolution of racemic epoxides has been published.24 The review also discusses the reactions of chiral bases with epoxides that give allylic alcohols. 

Nevertheless, adding H- to the carbon atom of a C=0 group would be a very useful reaction, as the result would be the formation of an alcohol. This process would involve going down from the aldehyde or ketone oxidation level to the alcohol oxidation level (Chapter 2, pp. 25-36) and would therefore be a reduction. It cannot be done with NaH, but it can be done with some other compounds containing nucleophilic hydrogen atoms. 

The azide procedure for peptide synthesis and particularly for fragment condensations is considered to be a mainly racemization free method. This low racemization tendency of azides was explained by several theories, which have been reviewed.t l The most plausible cause of racemization is the formation of oxazoles (Scheme 3) and the related enolization. In presence of bases the a-carbon proton is readily abstracted to form an anionic oxazol-5(4//)-one resonance system.For the formation of the oxazol-5(4//)-one the influence of the substituent Y on the a-carbonyl is essential. Since the a-carbonyl group of amino acid azides are less activated and thus relatively insensitive to oxygen containing nucleophiles such as water and alcohols, oxazol-5(4//)-one formation is largely prevented. It was proposed that the soft electron shell of the azide shields the a-carbonyl atom, so that only strong nucleophiles can attack it.t 1 The reactivity towards amines can be explained in a manner analogous to the aminolysis of anchimerically assisted active esters.h 1... 

A number of reactions of nitrogen-containing nucleophiles with aldehydes and ketones involve addition of the nitrogen to the carbon of the carbonyl group, followed by elimination of water to produce a double bond. Common examples are reactions of primary amines to produce substituted imines, reactions of secondary amines to produce enamines, reactions of hydrazine or substituted hydrazines to produce hydrazones, reactions of semicarbazides to give semicarbazones, and reactions of hydroxylamine to produce oximes. Usually these reactions are run with an acid catalyst. 

The usefulness of enamines stems from the fact that they contain nucleophilic carbon. The electrons responsible for this nucleophilicity are, in the final analysis, the (formally) unshared pair on nitrogen but they are available for nucleophilic attack by carbon of the enamine. Thus, in alkylation ... 

Starting material The principal carbon containing compound at the start of a synthetic route. If two or more carbon containing compounds are of approximately the same size, then the designation is usually based upon which molecule is the nucleophile. 

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