Insertion, alkenes/alkynes

Similarly to alkenes. alkynes also insert. In the reaction of 775 carried out under a CO atmosphere in AcOH, sequential insertions of alkyne, CO. alkene. and CO take place in this order, yielding the keto ester 776[483]. However, the same reaction carried out in THF in the presence of LiCl affords the ketone 777, but not the keto ester[484]. The tricyclic terpenoid hirsutene (779) has been synthesized via the Pd-catalyzed metallo-ene carbonylation reaction of 778 with 85% diastereoselectivity as the key reaction[485], Kainic acid and allo-kainic acid (783) have been synthesized by the intramolecular insertion ol an alkene in 780, followed by carbonylation to give 781 and 782[486],... 

Both these hydrides insert alkenes and alkynes the crystal structure of [Rh(NH3)5(C2H5)]2+Br2 shows the ethyl group has a trans-influence comparable to that of the hydride [93]. 

A related unprecedented double insertion of electron-deficient alkynes has also been reported in the reactions of the linear Pt2Pd heterotrimetallic complex 64 with 65 (RO2CCSCR) (Scheme 24) [95,96]. A series of unsymmetri-cal A-frame clusters 68 has thus been obtained in which a first insertion of the alkyne takes place site-selectively into the Pt-Pd bond vs the Pt-Pt bond (66). After a zwitter-ionic polar activation of the resulting inserted alkene (67), a subsequent reaction with the phosphine unit of the dpmp allows one to obtain the products 68 via the nucleophilic migration of the terminal P atom from the Pd center to the CH terminal carbon (formation of the P-C bond). 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

Diazoacetic esters, reactions with alkenes, alkynes, heterocyclic and aromatic compounds, 18, 3 26, 2 a-Diazocarbonyl compounds, insertion and addition reactions, 26, 2 Diazomethane ... 

A number of transition metal complexes react with alkenes, alkynes and dienes to afford insertion products (see Volume 4, Part 3). A general problem is that the newly formed carbon-metal bond is usually quite reactive and can undergo a variety of transformations, such as -hydride elimination or another insertion reaction, before being trapped by an electrophile.200 Usually, a better stability and lower reactivity is observed if the first carbometallation step leads to a metallacycle. It is worthy to note that the carbometallation of perfluorinated alkenes and alkynes constitutes a large fraction of the substrates investigated with transition metal complexes.20015... 

Full details42 have been published on the conversion of enynes into iminocyclopentenes using a titanium precatalyst in the presence of BuLi and TESCN (equation 9) the resulting iminocyclopentenes can be hydrolysed to cyclopentenones or reduced to allylic silyl-amines. In a related protocol43, the tandem insertion of TMSCN and alkenes, alkynes, ketones or isocyanates into zirconacyclo-pentanes or -pentenes leads to cyclopentylamines carrying an a-alkyl, -alkenyl, -1-hydroxyalkyl or -carboxamide substituent, respectively (equation 9). 

Oxidative cyclization is another type of oxidative addition without bond cleavage. Two molecules of ethylene undergo transition metal-catalysed addition. The intermolecular reaction is initiated by 7i-complexation of the two double bonds, followed by cyclization to form the metallacyclopentane 12. This is called oxidative cyclization. The oxidative cyclization of the a,co-diene 13 affords the metallacyclopentane 14, which undergoes further transformations. Similarly, the oxidative cyclization of the a,co-enyne 15 affords the metallacyclopentene 16. Formation of the five-membered ring 18 occurs stepwise (12, 14 and 16 likewise) and can be understood by the formation of the metallacyclopropene or metallacyclopropane 17. Then the insertion of alkyne or alkene to the three-membered ring 17 produces the metallacyclopentadiene or metallacyclopentane 18. 

The insertion of alkene to metal hydride (hydrometallation of alkene) affords the alkylmetal complex 34, and insertion of alkyne to an M—R (R = alkyl) bond forms the vinyl metal complex 35. The reaction can be understood as the cis carbometallation of alkenes and alkynes. 

The alkyne insertion reaction is terminated by anion capture. As examples of the termination by the anion capture, the alkenylpalladium intermediate 189, formed by the intramolecular insertion of 188, is terminated by hydrogenolysis with formic acid to give the terminal alkene 192. Palladium formate 190 is formed, and decarboxylated to give the hydridopalladium 191, reductive elimination of which gives the alkene 192 [81]. Similarly the intramolecular insertion of 193 is terminated by transmetallation of 194 with the tin acetylide 195 (or alkynyl anion capture) to give the dienyne 196 [82], Various heterocyclic compounds are prepared by heteroannulation using aryl iodides 68 and 69, and internal alkynes. Although the mechanism is not clear, alkenylpalladiums, formed by insertion of alkynes, are trapped by nucleophiles... 

Treatment of j]2-iminosilaacyl complex 6c with LiEt3BH gave azazircona-cyclopropane 10, which was hydrolyzed to give (silylmethyl)aniline in 82% yield (Scheme 5). Treatment of 10 with 4-octyne gave alkene 12 in 73% yield after hydrolysis. Presumably, the insertion of alkyne into the carbon-zirconium bond of 10 gives silazirconacyclopentene 11. When CuCl and allyl chloride were added to a THF solution of silazirconacyclopentene 11, tetrasubstituted alkene... 

There are implications for both alkyne polymerisation and alkene metathesis in the above observations. The sequence ( M2MU) comprises the transformation of one p-carbene to another vi an alkyne insertion followed by rearrangement. If one envisages a molecule of alkyne in the role played by CO in the (Hlj) conversion then the sequence can be taken a step further through insertion of alkyne into the new p-carbyne. Successive insertions and rearrangements of this type then provide a mechanism... 

Alkyl iridium compounds are also accessible via insertion (see Migratory Insertion) of alkenes into Ir H bonds. Analogously, alkenyl iridium compounds may be formed via insertion of alkynes into Ir-H bonds. These types of reactions have been studied to shed tight on the mechanism of alkene and alkyne hydrogenation processes. For example, HIr(CO)(PPh3)2 (65) will react with ethylene and higher olefins to produce the alkyl iridium compounds (equation 17). 

The reactivity of the cationic Zr complexes is a direct consequence of their Lewis acidity see Lewis Acids Bases) (i) various substitution reactions can occur into the Zr-solvent weak bond, (ii) unsatnrated substrates (CO, alkenes, alkynes, or ketones) insert into the Zr-C bond, potentially leading to polymerization reactions (see Section 8.2), (iii) new organic ligands obtained after reaction in the coordination sphere of the metal can be spontaneously released by /3-H elimination see -Hydride Elimination), or (iv) C-H bond activation of suitable ligands can occur. 

Ligand insertion often accompanies transfer of the organic moiety from the organomercurial, and stable, new transition-metal organometallics are isolated. This is especially true when the metal is Pd or Pt and the ligand is an alkene, alkyne, isonitrile or carbon monoxide ... 

Hydroamination/bicyclization of aminodialkenes, aminodialkynes, and amino-alkenynes opens a straightforward route to pyrrolizidines and indolizidines in a tandem C-N and C-C bond forming process. An important prerequisite for the success of this reaction sequence is a sufficient lifetime of the rare-earth metal alkyl intermediate formed in the initial insertion process of the alkene/alkyne in the Ln-amide bond in order to permit the carbocyclization step (Scheme 9) [99,174],... 

Reactions of this type are postulated as equilibria in synthetically important insertion reactions of alkenes, alkynes and other unsaturated molecules into the Pd-C bonds of dimeric palladacycles.271,272 Further, this reaction can form the basis for... 

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