Polar addition multiple bonds activated

It should be noted that formation of trans-product can be achieved in an anti-addition reaction through the outer-sphere mechanism. Theoretical studies have demonstrated that syn-addition and anti-addition reactions may start from the same 7i-complex, and direction of the multiple bond activation depends on the polarity of solvent [17, 18]. Relative reactivity in the inner-sphere and outer-sphere mechanisms contributes to the overall -/Z- selectivity of the addition reaction to alkynes (stereoselectivity issue). In some cases it is possible to switch the direction of C-Het bond formation by finding a suitable ligand [19]. In case of alkenes syn-addition and a f -addition processes do not necessarily result in different stereochemistry (unrestricted rotation around the single C-C bond in the product). Occurrence of these mechanisms for the N [20, 21], P [22, 23], O [24-26], S, Se [27, 28] heteroatom groups and application of different metal catalysts are discussed in detail in the other chapters of this book. Stereochemical pathways of nucleometallation and development of enantioselective catalytic procedures were reviewed [29]. In this chapter we focus our attention on the mechanism of irmer-sphere insertion reaction involving double and triple carbon-carbon bonds. 

Now, some addition reactions will be considered, the solvent dependences of which have been reviewed [77, 78]. Addition of uncharged electrophiles [e.g. Br2, ArS—Cl, NO—Cl, R—CO3H) to carbon-carbon multiple bonds leads to the development of a small, usually dispersed charge in the activated complex. In more polar solvents, this is accompanied by a slight rate acceleration. In reactions with substantial charge development in the activated complex, larger rate accelerations with increasing solvent polarity are observed. 

Active methylene compounds can be added to polar double bonds such as those in acrylate esters and methyl vinyl ketone as has been described in the previous section. Active methylene compounds can also be added to carbon-carbon multiple bonds in allenes and alkynes with the aid of the transition metal complexes as the catalyst. The addition of methylmalononitrile to 3-phenyl-l,2-butadiene takes place in the presence of Pd2(dba)3-CHCl3 to give the corresponding addition product with E-stereochemistry (Eq. 67) [137 a]. The C-C bond formation occurs exclusively at the terminal position of the allenes. Trost et al. independently reported the similar results with respect to palladium-catalyzed addition of C-H bonds in active methylene compounds to allenes [137 b. ... 

The ease of reaction depends both on the CH acidity of the addend and on the polarizability of the ethylenic double bond of the acceptor. Thus, in general, only such compounds function as addend in which a methylene or methine group is activated by two neighboring carbonyl or nitrile groups, as, for example, in malonic esters, malonodinitrile, cyanoacetic esters, 1,3-dioxo compounds and 3-oxo carboxylic esters, and their monoalkyl substitution products. The ethylenic double bond of the acceptor is polarized by conjugation with a polar multiple bond, so that the olefinic component is usually an unsaturated ketone, an, / -unsaturated ester, or an, / -unsaturated nitrile. The addition is catalysed by bases such as potassium hydroxide solution, sodium ethoxide, and amines. 

The recent developments on the metallation chemistry of oxazoles and benzoxazoles, isoxazoles and benzisoxazoles, pyrazoles and indazoles, thiazoles and benzo-thiazoles, and isothiazoles, benzo[c]isothiazoles, and benzoMisothiazoles have been reviewed. The two-decade history of catalytic carbon-carbon bond formation via direct borylation of alkane C-H bonds catalysed by transition metal complexes has been reported. The alkane functionalization via electrophilic activation has been underlined. " Recent advances of transition-metal-catalysed addition reactions of C-H bonds to polar C-X (X=N, O) multiple bonds have been highlighted and their mechanisms have been discussed. The development and applications of the transition metal-catalysed coupling reactions have been also reviewed. - ... 

Metals with a d f" configuration, group 3 metals, lanthanides, and actinides, are usually classified as f-elements. Because they are highly electropositive, they form polarized bonds with p-block elements, including carbon and nitrogen. So far, two reaction mechanisms have been established for d f metals cr-bond metathesis, a 2o—2o process, and 1,2-addition, a [2ct—2jt] process (2cr stands for the two electrons involved in the transition state that come from a tr bond and 2jt indicates the two electrons involved in the transition state that come from a Jt bond) (Scheme 1). " Oxidative addition, another type of reaction mecharusm that is common for late transition metals, is absent from the chemistry of rare-earth metals or actinides. This is partly because of the lack of valence electrons, i.e., a d electronic configuration however, even for uranium, which has multiple accessible oxidation states, no genuine oxidative addition reactivity has been reported. The subject of C—H bond activation mediated by f-elements has been dis-cussed by several recent reviews. ... 

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