Terminal olefin moiety

As a typical case, olefin-metal complexation is described first. Alkene complexes of d° transition metals or ions have no d-electron available for the 7i-back donation, and thus their metal-alkene bonding is too weak for them to be isolated and characterized. One exception is CpfYCH2CH2C(CH3)2CH=CH2 (1), in which an intramolecular bonding interaction between a terminal olefinic moiety and a metal center is observed. However, this complex is thermally unstable above — 50 °C [11]. The MO calculation proves the presence of the weak metal-alkene bonding during the propagation step of the olefin polymerization [12,13]. 

Hexadiene is also found to undergo extremely selective dehydrogenative silylation in the presence of a catalytic amount of RhCl(PPh3)3 at the terminal olefin moiety to... 

With nonconjugated dienes, the terminal olefin moiety reacts preferentially with both Pt and Rh catalyst systems (Eqs. 11, The reaction of ( , E, Z)-... 

Later, the groups of Sakai and of Tanaka and Suemune, respectively, extended the scope of the enantioselective cyclizations by employing desymmetrization of the aldehyde substrates bearing two identical terminal olefin moieties, and the cyclopentanone products with two vicinal stereo-centers, 8 or 9, could be obtained using a catalytic amount of the cationic Rh complex (5 mol%) (Table 8.2). However, if neutral Rh catalysts were employed, a high catalyst loading at 50 mol% was needed (entries 1, 2). Tanaka, Suemune, and co orkers also developed the kinetic resolution of unsymmetrical racemic diene-aldehyde 10 via a Rh-catalyzed asymmetric hydroacylation reaction (Scheme 8.5). The cyclization product could be obtained in >95% ee. ... 

In the case of nitronates possessing ester or nitrile moieties as terminal olefin substituents, tandem Michael addition to produce substituted furans 174,175 occurred faster than trapping of the nitronate anion by TMSCl (Eq. 17). 

Collman et al.99 reported the asymmetric epoxidation of terminal olefins catalyzed by iron porphyrin complex 129. The catalyst was synthesized by connecting binaphthyl moieties to a readily available aa/ / -tetrakis(aminophenyl)-porphyrin (TAPP). Epoxidation of unfunctinalized olefins was carried out using iodosylbenzene as the oxidant. As shown in Scheme 4-46, excellent results were... 

In this proposed process, p-hydride elimination first yields a putative hydride olefin rc-complex. Rotation of the -coordinated olefin moiety about its co-ordination axis, followed by reinsertion produces a secondary carbon unit and therefore a branching point. Consecutive repetitions of this process allows the metal center to migrate down the polymer chain, thus producing longer chain branches. Chain termination occurs via monomer assisted p-hydrogen elimination, either in a fully concerted fashion as illustrated in Figure 2b or in a multistep associative mechanism as implicated by Johnson1 et al. 

P-Cyclodextrin was modified by attaching 2-(diphenylphosphinoethyl)-thio- (127) and 2-bis(diphenylphosphinoethyl)amino- (126) moieties at the C-6 position [8-11]. The resulting macroligands were reacted with [ RhCl(NBD) 2] to provide the corresponding cationic rhodium-bisphosphine complexes. These catalysts showed pronounced selectivity due to complexation of the substrate by the CD unit adjacent to the catalyticaUy active metal center. For example, in competitive hydrogenation of similarly substituted terminal olefins (Scheme 10.4), 4-phenyl-but-l-ene was... 

The heteroatom-tethered enynes, If-i, were converted to the corresponding bicyclic heterocycles 2f-i without event, thereby further illustrating the scope of this transformation. The [RhCl(CO)2]2-catalyzed PK reaction with the 1,6-enynes Ij and Ij, which have a methyl group at a terminal position of the olefin moiety, furnishes the corresponding bicyclopentenone 2j and 2j in good to excellent yield. Interestingly, treatment of 1 j with a phosphine ligand-bound catalyst, such as 10, affords a mixture of the desired cyclopentenone 2j with the cycloisomerization product 2j (Eq. 1). 

Itami and Yoshida reported an elegant surrogate for terminal olefins, dimethyl(2 pyridyl)-vinylsilane 48. Since the reaction proceeds through a pre-complexation of Ru with the pyridine moiety, the outcome is regioslective to provide the products with the R locating at the / -positon from carbonyl (Equation (22)). This approach allows us to obtain products from any terminal olefins with well-defined regiochemistry. ... 

The thus-formed peroxide then adds to the end of the eneone. Ozonization of the terminal olefin then leads to the aldehyde (63-5). The newly formed carbonyl group is then reacted with the ylide from phosphonium salt (63-6) under salt-free conditions. This results in the addition of the f7W-trifluoromethylbenzyl moiety with cis geometry about the double bond. There is thus obtained arteflene (63-7) [72]. 

Vinyl sulfones in general serve as excellent dienophiles in Diels-Alder reactions,4 and we5 and others2-4 have found the resultant cyclohexene to contain very useful functionality for further manipulation. Hence the vinyl sulfone moiety can serve as a synthon for ethylene,6 terminal olefins,7 acetylene,8 and vinylsilanes9 in [4+2]-cycloadditions as well as valuable synthetic intermediates in general.10... 

An Olefin Moiety in the Presence of Terminal Alkyne Function... 

A dramatic improvement in this new round trip radical domino processes developed by Curran s group was presented by Takasu, Ihara and coworkers. The new method relies on the introduction of a conjugated ester moiety at the terminal olefin, thereby effecting an acceleration of the domino reaction accompanied with an enhancement of the regio- and stereoselectivity [81]. Thus, reaction of 3-196 with Bu3SnH led to a 4 3 mixture of the two diastereomeric tricycles 3-197 and 3-198 in 83 % yield. In this process, the vinyl radical 3-199 is initially formed, but this smoothly cyclizes in 5-e%o-trig manner to give radical 3-200 (Scheme 3.52). Due to... 

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