Nucleophiles additions to CO and

Self-consistent field molecular orbital calculations by Fenske and coworkers have confirmed that nucleophilic additions to Fischer and related complexes [e.g., (CO)sCr=CXY, (T)5-C5H5)(CO)2Mn=CXY], are frontier orbital-controlled rather than charge-controlled reactions (7-9). Interaction of the HOMO of the nucleophile with the carbene complex LUMO (localized on Ca) destroys the metal-carbon w-interaction and converts the bond to a single one. 

The asymmetric reactions discussed in this chapter may be divided into three different types of reaction, as (1) hydrometallation of olefins followed by the C—C bond formation, (2) two C C bond formations on a formally divalent carbon atom, and (3) nucleophilic addition of cyanide or isocyanide anion to a carbonyl or its analogs (Scheme 4.1). For reaction type 1, here described are hydrocarbonyla-tion represented by hydroformylation and hydrocyanation. As for type 2, Pauson-Khand reaction and olefin/CO copolymerization are mentioned. Several nucleophilic additions to aldehydes and imines (or iminiums) are described as type 3. 

At the beginning of the new millennium, Hashmi et al. presented a broad research study on both intramolecular and intermolecular nucleophilic addition to alkynes and olefins [18]. One of the areas covered by these authors was the isomerization of co-alkynylfuran to phenols [19]. After that, Echavarren and coworkers identified the involvement of gold-carbene species in this type of process, thus opening a new branch in gold chemistry [20]. And subsequently, Yang and He demonstrated the initial activation of aryl —H bonds in the intermolecular reaction of electron-rich arenes with O-nucleophiles [21, 22]. 

In the dehydrogenation of isobutyric acid, the by-products in addition to CO and C02 are propylene and acetone. Two reaction mechanisms were proposed (340, 341) and the latter is shown in Scheme 9 (340). The formation of methacrylic acid and acetone involves a common intermediate The El elimination of a proton from I yields the methacrylic acid while a nucleophilic SN1 attack of oxide ion produces C02 and acetone (344). On the other hand. 

Introduction. Ti-TADDOLates are a,a,a, a -tetraaryl-2,2-disubstituted l,3-dioxolane-4,5-dimethanolatotitanium derivatives. The most common substituents are R, R = Me/Me and Ph/Me, Ar=Ph and 2-naphthyl, X, Y = C1/C1, t-PrO/Cl, Cp/Cl, and i-PrO/i-PtO. The corresponding TADDOLs (2) are available in both enantiomeric forms from tartrate esters which are acetalized (R R CO) and allowed to react with aryl Grignard reagents. The reactions performed in the presence of Ti-TADDOLates or with Ti-TADDOLate derivatives include nucleophilic additions to aldehydes - - and nitroalkenes of alkyl, aryl, and allylic - groups aldol additions hydrophosphonylations and cyanohydrin reactions of aldehydes inter- and intramolecular Diels-Alder additions ... 

Linear Alkenes and Alkynes.— Nucleophilic addition to co-ordinated alkenes can either occur on the same side as the metal (cm attack) or on the side remote from the metal (trans attack) (Scheme 3). A study on the oxidative hydrolysis of alkenes in the... 

Various structural factors have been considered in interpreting this result The most generally satisfactory approach is based on a transition>state model, advanced by Felkin and co-woricers, in which the largest group is oriented perpendiculariy to the carbonyl group. Nucleophilic addition to the carbonyl groi occurs from the opposite side. ... 

Reaction of lithium 2,5-dimethylpyrrolate ion with [RhCl(CO)2]2 leads to formation of 84 (88PAC1193 90P1503). This is the first example of the mixed mode, when the ti N) and ti (C=C) coordination are realized simultaneously. Nucleophilic addition of triphenylphosphine and triphenylarsine gives 85 (E = P, As). The iridium analogs of 84 and 85 have also been synthesized. 

The effect of metal basicity on the mode of reactivity of the metal-carbon bond in carbene complexes toward electrophilic and nucleophilic reagents was emphasized in Section II above. Reactivity studies of alkylidene ligands in d8 and d6 Ru, Os, and Ir complexes reinforce the notion that electrophilic additions to electron-rich compounds and nucleophilic additions to electron-deficient compounds are the expected patterns. Notable exceptions include addition of CO and CNR to the osmium methylene complex 47. These latter reactions can be interpreted in terms of non-innocent participation of the nitrosyl ligand. 

Cyclopentadiene(diene)cobalt complexes, the largest catagory of diene complexes of Co, may be prepared by direct complexation, by preparation of the dienes within the coordination sphere of Co and by nucleophilic addition to ( j5-dienyl)CoCp cations. In comparison to (diene)CoCp complexes, there are considerably fewer examples of (diene)RhCp and (diene)IrCp complexes known. 

Nucleophilic addition to acyclic (diene)Mo+ cations has been examined. For (isoprene) Mo(CO)2L (L = Cp, Cp, In), the regioselectivity for nucleophilic attack has been found to depend on the nature of the nucleophile, the ligand L, the reaction solvent and the temperature21,813 833 193. The generation and in situ reactivity of transoid acyclic (diene)molybdenum and tungsten cations with nucleophiles has been previously mentioned (Section IV.C.2). 

Breslow and co-workers elucidated the currently accepted mechanism of the benzoin reaction in 1958 using thiamin 8. The mechanism is closely related to Lapworth s mechanism for cyanide anion catalyzed benzoin reaction (Scheme 2) [28, 29], The carbene, formed in situ by deprotonation of the corresponding thiazolium salt, undergoes nucleophilic addition to the aldehyde. A subsequent proton transfer generates a nucleophilic acyl anion equivalent known as the Breslow intermediate IX. Subsequent attack of the acyl anion equivalent into another molecule of aldehyde generates a new carbon - carbon bond XI. A proton transfer forms tetrahedral intermediate XII, allowing for collapse to produce the a-hydroxy ketone accompanied by liberation of the active catalyst. As with the cyanide catalyzed benzoin reaction, the thiazolylidene catalyzed benzoin reaction is reversible [30]. 

The most important application of organolithium reagents is their nucleophilic addition to carbonyl compounds. One of the simplest cases would be the reaction with the molecule CO itself, whose products are stable at room temperature. Recently, it was shown that a variety of RLi species are able to react with CO or f-BuNC in a newly developed liquid xenon (LXe) cell . LXe was used as reaction medium because it suppresses electron-transfer reactions, which are known to complicate the reaction . In this way the carbonyllithium and acyllithium compounds, as well as the corresponding isolobal isonitrile products, could be characterised by IR spectroscopy for the first time. 

As demonstrated in a series of kinetic experiments by Wittkopp and Schreiner, nitrone N-benzylideneanihne N-oxide can be activated for 1,3-dipolar cycloadditions through double hydrogen-bonding 9 [Ij. Takemoto and co-workers, in 2003, published the nucleophilic addition of TMSCN and ketene silyl acetals to nitrones and aldehydes proceeding in the presence of thiourea organocatalyst 9 (Figure 6.4) [147]. 

A formal asymmetric nucleophilic addition to carbonyl compounds is achieved by Trost and his co-workers in the allylic alkylation of acylals of alkenals. An excellent enantioselectivity is observed in this alkylation. The starting acylals are easily prepared by the Lewis-acid catalyzed addition of acid anhydrides to aldehydes, by use of Trost s ligand 118 (Scheme 13), where various carbon-centered nucleophiles are available (Scheme l4),101,101a-10lc Asymmetric synthesis of some natural products is achieved according to this procedure. 

The intermediate iis-cyclohexadienyl anionic species from nucleophilic addition to the [(arene)Cr(CO)3] complexes are obviously highly electron rich and should be susceptible to reactions... 

Nucleophile addition to styrene derivatives (e.g. 75) coordinated with Cr(CO)3 is another example of addition-electrophile trapping.23,128 Addition of reactive anions is selective at the 3-position of the styrene ligand, leading to the stabilized benzylic anion (76). The intermediate reacts with protons and a variety of carbon electrophiles to give substituted alkylbenzene ligands (in 77) (equation 52). 

Given that nucleophile addition to (dienyl)Fe(CO)3 complexes proceeds stereospecifically trans to the metal, the question arises as to whether this can be used to control relative stereochemistry during multiple functionalization of cyclohexadienes and cycloheptadienes. A hypothetical example is shown in Scheme 29, where nucleophile addition is followed by a second hydride abstraction, or its equivalent, to generate a substituted dienyl complex. Addition of a second nucleophile, assuming steieocontrol from the metal, would generate a disubstituted derivative with defined relative stereochemistry. 

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