Alkenes alkene insertion’ reaction

As a unique reaction of Pd(II), the oxidative carbonylation of alkenes is possible with Pd(ll) salts. Oxidative carbonylation is mechanistically different from the hydrocarboxylation of alkenes catalyzed by Pd(0), which is treated in Chapter 4, Section 7.1. The oxidative carbonylation in alcohol can be understood in the following way. The reaction starts by the formation of the alkoxy-carbonylpalladium 218. Carbopalladation of alkene (alkene insertion) with 218 gives 219. Then elimination of /3-hydrogen of this intermediate 219 proceeds to... 

The alka-l,2,4-trienes (ailenylaikenes) 12 are prepared by the reaction of methyl propargyl carbonates with alkenes. Alkene insertion takes place into the Pd—C bond of the ailenyipailadium methoxide 4 as an intermediate and subsequent elimination of/3-hydrogen affords the 1,2,4-triene 12. The reaction proceeds rapidly under mild conditions in the presence of KBr. No reaction takes place in the absence of an alkali metal salt[4j. 

Scheme 6.36. A Zr-catalyzed enantioselective alkene insertion reaction.

Organometallic compounds are used widely as homogeneous catalysts in the chemical industry. For example, if the alkene insertion reaction continues with further alkene inserting into the M C bond, it can form the basis for catalytic alkene polymerisation. Other catalytic cycles may include oxidative addition and reductive elimination steps. Figure above shows the steps involved in the Monsanto acetic acid process, which performs the conversion... 

The alkene insertion reaction is stereospecific only for singlet carbenes. For triplet carbenes, the reaction is nonstereospecific. Though carbenes formed thermally from diazoalkenes must initially be singlets, photochemistry is one way to provide the energy needed for their transformation to the more stable triplet. 

The palladium-catalyzed reaction of allyl chloride 11 with the benzyne precursor 104 to produces phenanthrene derivatives 131 is also known [83]. A plausible mechanism for this intermolecular benzyne-benzyne-alkene insertion reaction is shown in Scheme 38. Initially n-allyl palladium chloride la is formed from Pd(0) and 11. Benzyne 106, which is generated from the reaction of CsF and 104, inserted into la to afford the aryl palladium intermediate 132. A second benzyne insertion into 132 produce 133 and subsequent carbopalladation to the alkene afford the cyclized intermediate 134. f>- Iydride elimination from 134 followed by isomerization gave 9-methylphenanthrene 131. 

In some instances (<18VE) it is not always certain that nucleophilic attack occurs directly at the coordinated alkene, since attack at the metal centre followed by migration of the nucleophile to the alkene (alkene insertion, see below) may result in the same overall reaction product (Figure 6.8). 

In the absence of protons, the carbene is formed after loss of nitrogen and subsequent or concerted migration of hydrogen affords the alkene insertion reactions or migration of other groups can lead to side products. In the presence of protic solvents, a carbenium ion is formed via a diazonium ion this carbenium ion may then lose a proton to give the alkene or may give other reactions typical of carbenium ions. 

If a group, such as (C(0)0CH2CH2CH2CH=CH2), was used, the olefin was conforma-tionally constrained to bind perpendicular to the Pd—C bond and insertion-cyclization did not occur. Alkene insertion reactions into metal-acyl bonds usually occur more rapidly than insertions into metal-alkyl bonds. 

This mechanism is analogous to that proposed by Shephard and Rooney (95) for the isomerization of o-ethyltoluene to n-propylbenzene on platinum, a reaction which most likely involves a cyclopentane intermediate and was assumed to consist of an alkene-alkyl insertion reaction of a l,2n,5ff-triadsorbed precursor (Scheme 41). 

These intermediates undergo addition reactions with alkenes and insertion reactions with saturated systems. Addition also occurs on reaction with benzene. Many of the... 

Sol 1. (a) For singlet carbenes, the alkene insertion reaction is stereospecific. Therefore, the reaction of Z-but-2-ene with singlet carbene gives cis-1,2-dimethylcyclopropane. 

Organosilicon compounds are largely produced by the hydrosilylation of unsaturated organic substrates [47]. Various transition metal catalysts have been used to obtain alkyl-SiR products from the reaction of H-SiRj with an alkene. Alkene insertion into an M-Si bond is recognized as a fairly common process which plays a key role in catalytic hydrosilylation processes. The reaction of 1,3-butadiene (3-6) with triethylsilane in the presence of [Cr(CO)g] under photochemical condition yields exclusively the ds-1,4-adduct, ds-l-(triethylsilyl)-2-butene (7) (Scheme 10.7) [48]. In all cases, 1-4 addition products form in major, however, in some cases 1-2 addition product (9) also forms in minor yield. Formation of product 12 can be rationalized in terms of double bond migration subsequent to the initial hydrosilylation (Scheme 10.7). 

In 2012, Murakami et al reported the asymmetric intramolecular alkene insertion reaction of 3-(2-styryl)cyclobutanones catalysed by an in situ generated chiral nickel complex bearing a BINOL-derived phosphoramidite ligand 15 (Scheme 10.22). The reaction provided a unique and straightforward access to... 

Alkene insertion reactions also occurred with benzocyclobutenones [55]. Benzocyclobutenone 85 containing an alkene chain at the 6-position yielded the fused product 86 (Scheme 3.47). Use of a chiral ligand enabled enantioselective synthesis of benzotricyclic ketones in good enantiomeric excesses [56]. 

Murakami et al. reported a nickel-catalyzed alkyne/alkene insertion reaction into a C(carbonyl)-C(sp ) bond of cyclobutanones [21] and applied it to the enantioselective synthesis of benzobicyclo[2.2.2]octenones (Scheme 8.4) [22]. [2-f2] Cycloaddition of 1,2-divinylbenzene 24 with dichloroketene followed by... 

Cycloinumakiol is a diterpene isolated from podocarpus latifolius. The originally proposed structure was 36 with a tetracyclic dihydrofuran skeleton having a quaternary chiral carbon center at the benzylic position (Scheme 8.6). Dong et al. developed a rhodium-catalyzed site-selective alkene insertion reaction into a C-C bond of benzocyciobutenones [24], and applied it to the first total synthesis of 36 [25]. The synthesis led to the structural revision of cycloinumakiol. 

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