Insertion reactions alkene

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 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. 

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. 

Additional experiments with the same catalyst source showed further that addition of a base such as sodium acetate or sodium carbonate also promoted the syn-aminopalladation pathway. Obviously, under basic conditions, aminopalla-dation occurs through alkene insertion into a palladium amidato complex with a defined Pd-N bond [45]. Additional experiments by Stahl and White [46] employing an isolated palladium suUbnamidato complex and its intramolecular aminopallada-tion product suggested the alkene insertion reaction to be reversible in nature but to be turned over irreversibly in the presence of molecular dioxygen. Electronically enriched amidates favor the alkene insertion reaction. 

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... 

Often, insertion reactions involve, formally, H or H and may be difficult to distinguish from alkene insertion reactions of the type given above. Examples... 

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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