Olefin active

Enamines are readily alkylated by olefins activated by electron-withdrawing substituents. N Alkylation by one of these olefins is reversible, whereas C alkylation is not, so that a good yield of monoalkylated product is the rule. 

Although N-(2-phenylethyl)morpholine is formed in only 14% yield (TOE = 0.3 h ), this is the first example of a transition metal-catalyzed anti-Markovnikov hydroamination of a non-activated olefin. Concerning the reaction mechanism, labeling experiments led the authors to favor activation of the N-H bond over olefin activation [166]. 

Copper-olefin bonding is of both practical and theoretical interest in view of the catalytic activity of copper(I) toward olefin activation and its role in biological systems. 

Dicyclopropylallene reacts with olefins activated by ester groups at 200 °C to yield the adducts 20 predominantly (Table 12.1). In contrast, the reactions with methylenemalononitrile occurred at room temperature with selective production of the adduct 19 [18], A dipolar mechanism is assumed for the latter reaction. 

The radical addition of Cp2Br2 on olefins (activated or not) leads to difluorobro-momethyl and difluoromethyl compounds. ... 

Olefins activated by an electron-withdrawing group (Z may be C=C. halogen, C=0, Ar, CN, etc.) can be arylated by treatment with a diazonium salt and a cupric chloride3118 catalyst. This is called the Meerwein arylation reaction.3 Addition of ArCl to the double bond (to... 

In a reaction similar to 5-19, alkyl groups can be added to olefins activated by such groups as COR, COOR, CN, and even Ph.539 In the method illustrated above, the R group comes... 

This early example is one of the numerous synthetic utilizations of the cycloadditions of olefins activated by sulfur atoms at various oxidation levels (vinyl sulfides, sulfoxides and sulfones = -S(0) R, n = 0,1, 2). Most of the work carried out in this field has been pertinently reviewed and discussed in a 1988 Tetrahedron Report with 204 references [485], Some specific aspects are underlined here and recent examples given. 

Equation 12.15 illustrates another variation of the 2 + 2 reaction, the rr2 + o2 addition of olefins activated by electron-withdrawing groups to highly strained single bonds. (The wavy lines indicate a mixture of stereoisomers.) The lack of stereospecificity shows that these are stepwise reactions.33... 

The a-olefin activity is significantly decreased when both carbons in positions 3 and 4 are substituted for instance, the activity of 3,4-dimethyl-1-pentene is 5 times lower than that of 3-methyl-1-pentene, which, in turn, is 3 times lower than that of 4-methyl-1-pentene [37]. 

Metalloporphyrins catalyze the autoxidation of olefins, and with cyclohexene at least, the reaction to ketone, alcohol, and epoxide products goes via a hydroperoxide intermediate (129,130). Porphyrins of Fe(II) and Co(II), the known 02 carriers, can be used, but those of Co(III) seem most effective and no induction periods are observed then (130). ESR data suggest an intermediate cation radical of cyclohexene formed via interaction of the olefin with the Co(III) porphyrin this then implies possible catalysis via olefin activation rather than 02 activation. A Mn(II) porphyrin has been shown to complex with tetracyanoethylene with charge transfer to the substrate (131), and we have shown that a Ru(II) porphyrin complexes with ethylene (8). Metalloporphyrins remain as attractive catalysts via such substrate activation, and epoxidation of squalene with no concomitant allylic oxidation has been noted and is thought to proceed via such a mechanism (130). Phthalocyanine complexes also have been used to catalyze autoxidation reactions (69). 

Activity Good activity towards cyclic and acyclic olefins Highly active for linear olefins Highly active for simple olefins active for functionalized olefins when activated with R4Sn High activity for ROMP and RCM. Good reactivity for linear olefins, but slower when branched... 

Apart from these two examples, in the rest of the olefin activations, gold coordinates to the olefin, turning it susceptible to nucleophilic attack. The early examples of alkene functionalization by gold catalysis (equation 144) focused on the intermolecular addition of 1,3-diketones to styrenes. " An intramolecular version with ketoamides to yield pyrrolidinones was later developed and followed by the intermolecular addition of phenols (equation 145) and carboxylic acids to double bonds,a work that included an example of intramolecular addition of an aliphatic alcohol to an olefin. 

The coordination of olefins to gold species is well known, despite the preference for alkynes, allenes, and carbonyl groups. This is reflected in the fact that synthetic applications based on olefin activation by gold have been developed to a lesser extent than aUcyne or carbonyl activation. 

The last example included in this section is an oxidative cleavage of styrenes performed in water with tert-butyUiydroperoxide as the oxidant (equation 149). In this reaction, the first step is an olefin activation that should be followed by oxidation, although the mechanism is unknown. The catalyst employed is AuCl with neocuproine as the ligand. 

On the basis of kinetic data Mimoun proposes that the reaction takes place in two steps (i) coordination of the olefin in the vacant site trans to the 0x0 ligand (Fig. 8) followed by (ii) an intramolecular nucleophilic attack by dioxygen on the coordinated olefin. The coordination of the olefin activates it towards nucleophilic attack. The five membered dioxo-metalla cycle decomposes to give epoxide and Mo = O ... 

Ni(0) catalysis is able to induce reactions of methylenecyclopropane with olefins activated by electron-withdrawing groups (equation 193). These cycloadditions work with the utmost efficiency in the case shown, whereas more substituted components might give lower yields due to competing side reactions such as cyclo- and codimerization. These problems could be circumvented by employing new Ni(0) systems with triarylphosphines as cocatalysts (equation 193). Similar conditions lead to the smooth addition of dialkylmethylenecyclopropanes to electron-deficient olefins. ... 

Bellamy and Kerr reduced other olefin-activated cyclopropanes and obtained ringopening products, also with no dimers ... 

Compared with unactivated olefins, activated olefins with carbonyl groups are reduc-tively cyclized with slightly lower stereoselectivity [75,79-82]. 

Olefin activation by electron-withdrawing groups is no longer necessary when an intramolecular trapping is programmed because radical cyclizations occur faster than do intermolecular additions. In such cases, the stereoselectivity of the cyclization and its efficiency will depend on several parameters such as ring size, the type of atoms, and the nature of asymmetric centers present in the ring. 

William Christopher Zeise (1789-1847) was a Danish apothecary and professor in Copenhagen, Denmark. He synthesized the first metal-olefin complex by serendipity (this term is explained in Chapter 4), when he treated platinum(IV) chloride with ethanol and potassium chloride K[PtCl3( -C2H4)], sal kalico-platinicus inflammabilis , cf [73], TT-Complexation of olefins at transition metals nowadays comprises a key feature of homogeneous catalysis in terms of olefin activation, with the Wacker-Hoechst process being a prominent example (cf. Section 2.4.1). 

Several improved titanium-derived catalysts have been reported for the reductive coupling of carbonyls to diols and olefins, activated halides to alkanes and vic-dihalides to olefins.38 If0... 

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