Nucleophile intermediate

Two principle approaches from thiopyrylium salts to thiopyrans accompanied by C-substitution have been found, e.g., the one-step additions of C-nucleophiles or the two-step procedures involving primary conversions of the salts to nucleophilic intermediates followed by attacks with appropriate electrophiles. 

Formation of a bis-allylated product of 4-nitrobenzoyl chloride by the reaction with allyltrimethyltin in the presence of a benzylpalladium(ll) complex was observed by Stille and co-workers in 1983.4 Trost and King also reported allylation of aldehydes by allyltin reagents in 1990.456 However, the precise mechanism was unclear until the extended studies were performed by Yamamoto and co-workers since 1995.4S7,4S7a 4S7 Aldehydes and imines react with allyltin reagents in the presence of a palladium catalyst (Equations (95) and (96)), and imines are chemoselectively allylated in the presence of aldehydes (Equation (97)).4S7,4S7l 4 b Mechanistic studies using NMR spectroscopy proved that bis-7t-allylpalladium complex 203 is a key nucleophilic intermediate (Figure 3). 

The chemistry takes place via an initial reduction of vitamin B12 or a similar cobalt (III) species 275, in a process that sees the conversion of cobalt from the +3 to the -1-1 oxidation state, and the opening of two sites of unsaturation, to afford 276 [74], This very reactive, highly nucleophilic intermediate reacts rapidly with the alkyl halide to form the octahedral complex 277, and reestablish... 

When 1,3-dimethylorotic acid (233) was heated at 198 °C in benzyl bromide for 3h, 6-benzyl-1,3-dimethyluracil (236) was formed in 10% yield together with the product of decarboxylation, 1,3-dimethyluracil (235). This finding supports the involvement of a carbon-6-centred nucleophilic intermediate in the decarboxylation reaction a carbanion (234) could be involved or a carbene (237)." ... 

Decarboxylation of 1,3-dimethylorotic acid in the presence of benzyl bromide yields 6-benzyl-1,3-dimethyluracil and presumably involves a C(6) centered nucleophilic intermediate which could nonetheless have either a carbene or ylide structure. Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry has been used to explore the gas-phase reactions of methyl nitrate with anions from active methylene compounds anions of aliphatic ketones and nitriles react by the 5n2 mechanism and Fco reactions yielding N02 ions are also observed nitronate ions are formed on reaction with the carbanions derived from toluenes and methylpyridines. 

Examples have recently been reported of NHC-catalyzed internal redox processes that directly convert a-reducible aldehydes to cz-reduced amides [19, 20]. 17 is found to be an efficient species to accelerate C-N bond formation via the nucleophilic intermediate 19, as shown in Scheme 14.4. Very recently, a few examples. 

The key intermediate in the reduction of metal ions by carbon monoxide and water is the hydroxycarbonyl (18). Initially (18) was proposed to form by a migratory insertion of CO into a M—OH bond, but more recent studies have favored a direct attack of water or hydroxide on a coordinated carbonyl (4,62). This latter view is in accord with the expected reactivity of coordinated CO toward nucleophiles. Intermediate (18) may then decarboxylate to give C02 and either a reduced metal ion or a metal hydride, as in (29) and (30), respectively. 

Examples of cyclization through alkene insertion of a metal-nucleophile intermediate (Scheme 3, intermediate F) using organolanthanide catalysts, (Cp LaHfe, have been reported recently (equation 132), although turnover numbers rather than synthetic yields were reported.263... 

The mechanism is similar to other acid-catalyzed a halogenations the enol form of the acyl bromide serves as a nucleophilic intermediate. The first step is formation of acyl bromide, which enolizes more readily than does the acid. 

Enolates are useful nucleophilic intermediates which are frequently employed in synthesis particularly for the formation of the carbon-carbon bond. 

Alternatively, when the ketene is generated in the presence of triethylamine, one cannot exclude the formation of a nucleophilic intermediate (3) which would then add to the carbonyl compound (Scheme 1). 2... 

Trapping the carbonyl compound 1 in Scheme 3.3 with various nucleophiles provides various catalytic oxidative transformations of alcohols. When a primary or secondary amine is employed as a nucleophile, intermediate 13 undergoes nucleophilic reaction with amine to give iminium ion complex 14 along with water. Intramolecular hydride transfer of 14 gives the corresponding N-alkylated amine 15 with regen-... 

Mulholland and Richards [344-346] have carried out ab initio (MP2/6-31-i-G(d) and RHF/6-31+G(d)) and semiempirical (AMI, PM3 and MNDO) molecular orbital calculations focussing on the enzyme citrate synthase. Their calculations were performed on the first stage of the citrate synthase reaction [344], on the substrate oxaloacetate [345] and on a simple model of the condensation reaction [346]. Their aim was to model the nucleophilic intermediate produced by the rate-limiting step, to examine which form of acetyl-CoA is the likely intermediate and how it is stabilised by the enzyme. They have found that the enolate is the likely nucleophilic intermediate in citrate synthase being stabilised by hydrogen bonds. 

Reaction intermediates and transition state modelling can be realistically studied with the inclusion of the protein environment. This issue has been addressed by Mulholland and Richards ([390] and references therein) for the citrate synthase enzyme. While transition state and stable intermediate structures have been optimised at semiempirical and ab initio levels, these authors have also studied the reaction in the enzyme both with AMI QM/MM and with ab initio QM/MM calculations, which have indicated that the enolate of acetyl-CoA is the likely nucleophilic intermediate in citrate synthase, in agreement with the gas-phase findings [346]. One of the conclusions from the paper is the fact that semiempirical QM/MM simulations are likely to be able to provide further useful understanding of enzyme reactions. 

In low-water conditions, it is proposed that the promotional effects of iodide and acetate involve two competitive pathways between four-coordinate and five-coordinate nucleophilic intermediates for rate-determining reactions with CH3I (Scheme 2). 

Reduction of suitably oriented 1,3-diketones by alkali metal in ammonia solutions also generates reactive nucleophilic intermediates which are capable of intra- and intermolecular attack on electrophilic functions. 

Nucleophilic intermediates formed in the white phosphorus-hydroxide reaction are also trapped by electron deficient alkylating agents, such as acrylonitrile, acrylamide, ethyl acrylate or vinylphosphonate Reaction of... 

Hexafluoroacetone is not known to polymerize by a free radical mechanism, however, it reacts readily with nucleophilic reactants and can form copolymers via nucleophilic intermediates (13). Many of its derivatives create surfaces with low critical surface tensions ( ). It was theorized that in a mild glow discharge reaction, the carbonyl group could be activated and the C3FgO group might... 

Ring opening of azetidinesJ 3-Aminolithium reagents are obtained as nucleophilic intermediates. 

Exam )le Typical reagent Electrophile Nucleophile Intermediate Regiochemistry Stereochemistry Product... 

The most important palladium-catalyzed processes include Heck vinylation of halides and sulfonates and various cross-coupling reactions in which a nucleophilic intermediate (stannane, organo-zinc halide or boronic acid) is coupled with an electrophile (halide or sulfonate). These coupling reactions are usually restricted to arylation and vinylation because of the tendency of alkylpalladium species to undergo elimination. The pyrrole and indole rings can participate in cross-coupling as either the nucleophilic or electrophilic component. 

Finally, it has also to be mentioned that enolizable a,p-unsaturated aldehydes have also been employed as Michael donors in this context (Scheme 2.18). This reaction proceeds via formation of a dienamine nucleophilic intermediate, which undergoes regioselective a-addition leading to the formation of the corresponding Michael adduct containing an a-substituted p,y-unsatu-rated aldehyde moiety. The conditions had to be carefully optimized and required the use of a y,y-disubstituted a,p-unsaturated aldehyde reagent and involved the use of catalyst 31a in the presence of AcOH as Bronsted acid cocatalyst and acetonitrile as solvent. In situ reduction of the Michael adducts was... 

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