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Alkenes soft nucleophile

Another reaction occurs by the attack of a soft nucleophile at the central carbon to form the 7r-allylpalladium complex 7, which undergoes further reaction with the nucleophile typical of rr-allylpalladium complexes to form the alkene 8,... [Pg.454]

Dihydropyrroles have recently become readily available by ring-closing metathesis. For this purpose, N-acylated or N-sulfonylated bis(allyl)amines are treated with catalytic amounts of a ruthenium carbene complex, whereupon cyclization to the dihydropyrrole occurs (Entries 6 and 7, Table 15.3 [30,31]). Catalysis by carbene complexes is most efficient in aprotic, non-nucleophilic solvents, and can also be conducted on hydrophobic supports such as cross-linked polystyrene. Free amines or other soft nucleophiles might, however, compete with the alkene for electrophilic attack by the catalyst, and should therefore be avoided. [Pg.392]

The palladium-catalyzed Heck-type reaction of methylenecyclopropane 66 in the presence of soft nucleophiles such as sodium diethylmalonate gives a mixture of isomeric alkenes 70 and 71 (Scheme 8.32) [77]. In this process, there is first a carbopalladation of the double bond of 66 giving the cyclopropylcarbinylpalladium in-... [Pg.240]

Rozhkov IN, Borisov YA (1988) Relative reactivity of F-alkenes in regard to the hard-soft nucleophiles. The fifth regular meeting of soviet-japanese fluorine chemists, Tokyo, p 75... [Pg.36]

In general, though, it is very difficult to predict whether aqueous acid will hydrate the alkene or dehydrate the alcohol. The method we are about to introduce is much more reliable. The key is to use a transition metal to help you out. Alkenes are soft nucleophiles (p. 237) and interact well with soft electrophiles such as transition metal cations. Here, for example, is the complex formed between an alkene and mercury(II) cation. Don t be too concerned about the weird bond growing from the middle of the alkene this is a shorthand way of expressing the rather complex bonding interaction between the alkene and mercury. An alternative, and more useful, representation is the three-mem-bered ring on the right. [Pg.518]

Soft nucleophiles (Nu) generally give the best results so, for carbon-carbon bond formation, stabilized enolates such as malonates are best, but for C-X (X = O, N, S) bond formation the reaction is successful with alkoxides, amines, cyanide, and thioalkoxides. This example shows an amine attacking outside the ring probably because the alkene prefers to be inside the ring. [Pg.1331]

Alkenes, with a n orbital as the HOMO and no charge, are inherently soft nucleophiles, and their nucleophilicity ought to bear some relationship to the energy of their HOMOs. The relative rates of attack by different alkenes on several electrophiles have been measured, but most systematically, Mayr has measured the nucleophilicity of a wide range of alkenes 4.18 being attacked by a family of diarylmethyl cations 4.19.15... [Pg.118]

I. N. Rozhkov and Y.A. Borisov, Fifth Regular meeting of Soviet-Japanese Fluorine Chemists. Relative Reactivities ofF-Alkenes in Regard to the Hard-Soft Nucleophiles, Tokyo, 1988, p. 75. [Pg.229]

Alkynes are more susceptible than alkenes to external soft nucleophiles, as demonstrated in the reaction of (37) with formaldehyde, where an excess of Nal dramatic ly changes the cyclization mode (Scheme 20). ... [Pg.740]

For example, the reaction between the soft nucleophile, e g. an alkene, and a soft electrophile, such as a bromine molecule, is shown in the following reaction. [Pg.134]

To take a very simple example, a nucleophile like the hydroxide ion is hard at least partly because it has a charge, and because it is based on a small and electronegative element. Accordingly, it reacts much faster with a hard electrophile like a proton than with a soft electrophile like bromine. On the other hand, an alkene is a very soft nucleophile, at least partly because it is uncharged and has a high-energy HOMO. Thus it reacts much faster with an electrophile which... [Pg.36]

Interception of the Tr-allyl palladium complex by soft nucleophiles, particularly malonates, has been described above. Alkenes, alkynes and carbon monoxide can also insert into the Tr-allyl palladium complex, generating a u-alkyl palladium species. When an internal alkene is involved, a useful cycbzation reaction takes place (sometimes called a palladium-ene reaction).Addition of palladium(O) to the allylic acetate 225 gave the cyclic product 226 (1.225). The reaction proceeds via the -ir-allyl palladium complex (formed with inversion of configuration), followed by insertion of the alkene cis- to the palladium and p-hydride elimination. In some cases it is possible to trap the a-alkyl palladium species with, for example, carbon monoxide. [Pg.101]

The mixed phosphonium-iodonium ylides (Section 2.1.10.1), such as the tosylate 796, represent a useful class of reagents that combine in one molecule the synthetic advantages of a phosphonium ylide and an iodonium salt [1091-1100]. Specifically, phosphorane-derived phenyliodonium tosylate 796 reacts with soft nucleophiles, such as iodide, bromide, benzenesulfinate and thiophenolate anions, to form selectively the respective a-functionalized phosphonium ylides 797 (Scheme 3.315), which can be further converted into alkenes (e.g., 798) by the Wittig reaction with aldehydes [1092]. The analogous arsonium-iodonium ylides have a similar reactivity toward nucleophiles [1091, 1094, 1101]. [Pg.282]

The catalytic cycle for stabilised or soft nucleophiles (which are the conjugate bases of acids whose pKi, is lower than 25) involves the direct attack of the nucleophile on the alkene coordinated to palladium. Part of the mechanism for substrate 11 is depicted in Scheme 8.5. [Pg.450]

The reactions discussed so far involved attack of soft nucleophiles on rr-alkene palla-dium(II) complexes. Hard carbon nucleophiles such as methyl lithium also react with these complexes.f The alkylation proceeds here by initial attack at the palladium atom. Subsequent di-insertion of the olefin into the Pd—C bond and di-/S-hydride elimination result in liberation of the alkylated alkene. The arylation of styrene by Grignard reagents can also be performed,the reaction being realized in the presence of stoichiometric or catalytic quantities of palladium chloride (Scheme 14). [Pg.608]

Activation of Carbon-Carbon r-Bonds. The title compound can form adducts with unpolarized jr-systems, allowing the addition of soft nucleophiles. The addition of /3-dicarbonyls onto alkynes is the most reported instance of this type of reaction, with both intramolecular and intermolecular examples. Welding grade acetylene can even be used as the alkene substrate (eq 35). Imines can also be used as nucleophiles, and then a second nucleophile such as an allylstannane can react with the intermediate iminiumto yield dihydroisoquinolines (eq 36). ... [Pg.359]


See other pages where Alkenes soft nucleophile is mentioned: [Pg.409]    [Pg.409]    [Pg.1108]    [Pg.1117]    [Pg.238]    [Pg.1528]    [Pg.109]    [Pg.2049]    [Pg.238]    [Pg.238]    [Pg.270]    [Pg.129]    [Pg.142]    [Pg.184]    [Pg.4]    [Pg.238]    [Pg.1529]    [Pg.256]    [Pg.2047]    [Pg.2048]    [Pg.64]    [Pg.13]    [Pg.87]    [Pg.313]   
See also in sourсe #XX -- [ Pg.109 ]




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