Nucleophilic Additions to Olefins

The stereochemical outcomes of the above reactions can be explained by the proposed transition states A and B (Fig. 2.25). Model A, derived from the Houk model for nucleophilic addition to olefins, explains the formation of, v y -adducts. Model B, involving a different nitrone conformation, due to the chelation of diethylaluminum chloride, accounts for the formation of anti -adducts (581). 

C. E Bemasconi, Nucleophilic Addition to Olefins. Kinetics and Mechanism, Tetrahedron 1989, 45, 4017-4090. 

C. F. Bernasconi, Nucleophilic addition to olefins. Kinetics and mechanism, Tetrahedron 1989, 45,4017-4090. 

Examples of substrate-induced 1,2 diastereoselection have been recorded for [2,3] rearrangements of allylic ethers 12 which possess an additional allylic oxygen substituentl0-15. The observed diastereofacial selectivity is consistent with theoretical models78 which predict that stercoelectronically favored conformations for intramolecular nucleophilic addition to olefin 12 will be those for which the allylic CO cr-bond is coplanar with the 7 -system of the olefin, maximizing n-transition state. Of the two conformers which satisfy this stereoelectronic requirement, the isopropyl outside orientation, which minimizes steric interactions of the allylic substituent, predominates and is reflected in the observed diastereoselection of the rearrangement15. 

Imbalance as a Function of X and Y. Nucleophilic additions to olefins also show imbalances in the structure-reactivity coefficients. In analogy to the proton transfers, I = anucn — (3nucn is defined as a measure of the imbalance Pnucn is the normalized Pnuc value 4 for anucn (measure of negative... 

Table IV. anucn and pnucn Values in Nucleophilic Additions to Olefins...

The Pd(ll)- and Pt(ll)-promoted nucleophilic additions to olefins are important reactions in organic synthesis. Nucleophiles that have been shown to add to coordinated olefins include OH , RO , AcO , CP, amines, and amides, and with the possible exception of OH", nucleophilic attack takes place on the side of the double bond remote from the metal. The main difference between Pd(ll)- or Pt(Il)-promoted and Fe(II)-promoted addition is that nucleophilic attack on Pd(ll)- or Pt(II)-coordinated monoolefins results in reduction of the divalent metal to the zero valent state. In most cases, Pd(ll) salts promote nucleophilic attack on olefins more readily than Pt(II) salts (Hartley, 1973 Maitlis, 1971). Equations (97) (Stern and Spector, 1961), (98) (Baird, 1966), (99) (Kitching et al., 1966), (100) (Akermark et al., 1974), and (101) (Kohl and Van Helden, 1968 Henry, 1972) illustrate some typical Pd(ll)- and Pt(II)-promoted additions to olefins. 

Trifluorothioacetic acid undergoes free-radical and nucleophilic addition to olefins and ketones respectively, paralleling in many ways the well-known reactions of thioacetic acid. Novel uses of thiolesters in synthesis... 

Despite the successes of the gold-catalyzed addition of O-nucleophiles to alkynes, the corresponding catalyzed reactions involving nucleophilic addition to olefins are very limited. Mild, metal-catalyzed additions of O-H bonds across olefins have been studied for decades, and efforts to develop such processes have intensified in the last years. Results of the hydroalkoxylation of alkenes are collected in different reviews [1, 94-96, 161]. 

Pd(II) compounds coordinate to alkenes to form rr-complexes. Roughly, a decrease in the electron density of alkenes by coordination to electrophilic Pd(II) permits attack by various nucleophiles on the coordinated alkenes. In contrast, electrophilic attack is commonly observed with uncomplexed alkenes. The attack of nucleophiles with concomitant formation of a carbon-palladium r-bond 1 is called the palladation of alkenes. This reaction is similar to the mercuration reaction. However, unlike the mercuration products, which are stable and isolable, the product 1 of the palladation is usually unstable and undergoes rapid decomposition. The palladation reaction is followed by two reactions. The elimination of H—Pd—Cl from 1 to form vinyl compounds 2 is one reaction path, resulting in nucleophilic substitution of the olefinic proton. When the displacement of the Pd in 1 with another nucleophile takes place, the nucleophilic addition of alkenes occurs to give 3. Depending on the reactants and conditions, either nucleophilic substitution of alkenes or nucleophilic addition to alkenes takes place. 

Because of their relative instabiUty, primary phosphine oxides caimot be isolated and must be converted direcdy to derivatives. Primary and secondary phosphine oxides undergo reactions characteristic of the presence of P—H bonds, eg, the base-cataly2ed nucleophilic addition to unsaturated compounds such as olefins, ketones, and isocyanates (95). 

The chemical reactions of sulphonyl nitrenes include hydrogen abstraction, insertion into aliphatic C—H bonds, aromatic substitution , addition to olefinic double bonds, trapping reactions with suitable nucleophiles, and Wolff-type rearrangement. Hydrogen-abstraction from saturated carbon atoms is usually considered to be a reaction typical of triplet... 

It is noteworthy that the nature of the ionic intermediate formed in bromine addition to olefins and the solvent properties also govern the competition between nucleophilic trapping and elimination. Thus 1,1-diphenylethylene, 11, gives the corresponding dibromide 13 (or solvent incorporated products, 14) and vinyl bromide, 12, in a ratio changing from 99 1 to 5 95 depending on solvent and on bromine concentration.(20) (see Table III results)... 

Lifetimes of the ionic intermediates of nucleophilic substitution are generally correlated to the pathways followed under given reaction conditions. Information on the lifetimes of ionic intermediates formed by bromine addition to olefins in methanol, as determined by the azide clock method, do not allow the different reaction pathways to be distin-... 

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]. 

The mechanism involves nucleophilic addition to a Z-substituted olefin followed by an intramolecular bimolecular nucleophilic substitution. Several side reactions also occur. Discuss the chemistry involved in this reaction, pointing out substituent effects at each stage. 

Palladium (II)-Nucleophile Addition across Olefins. Adding palladium complexes to olefins, either in the presence of an external nucleophile or a ligand which is attached to palladium, produces a palladium-carbon sigma-bonded complex which is not usually isolated in the case of monoolefins. Instead it decomposes and in doing so oxidizes the olefin to an organic carbonyl compound or a vinyl compound, exchanges a substituent group on the olefin, isomerizes the double bond, arylates (alkylates) the olefin, or carboxylates the olefin (2, 3). 

A variety of organic reactions, including dehydration of alcohols, cleavage of ethers, many additions to olefins, a number of nucleophilic substitutions, and various rearrangements, are catalyzed by acids. Since the substrates in these... 

A second characteristic reaction of carbenes is addition to olefins to yield cyclopropanes. Singlet carbenes might react as either nucleophiles or electrophiles triplets may be expected to behave like free radicals- The data in Table 5.9, showing the increase in rate of addition on substitution of electron-donating... 

Tungsten j4-diene cations in both s-trans and s-cis forms have been synthesized and the influence of the diene conformation on the regiochemistry of nucleophilic attack has been demonstrated488. Application of nucleophilic additions to Mo-complexed olefins in the construction of quaternary carbon centres has been summarized489. 

B2. With Neutral Molecules Electron Transfer Addition to Olefins Cycloaddition to Diolefins Complex Formation B3. With Ions or Dipolar Substrates Nucleophilic Capture B4. With Radicals Spin Labeling Oxygenation (302)... 

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