Tandem Olefin Metathesis

Grubbs has reported a similar tandem olefin metathesis-carbonyl olelination process for the preparation of cyclic olefins [31]. In this case, treatment of a keto-olefin with the molybdenum alkylidene 1 at 20°C generates an intermediate alkylidene complex. Under these conditions, competing intermolecular olelination does not occur. However, intramolecular carbonyl olelination of the initially formed alkylidene complex can occur and this results in the formation of a cyclic olefin. This tandem sequence is illustrated by the transformation of keto-olefins... 

Azabicyclononenecarboxylate acylated with unsaturated carboxylic acids is converted via tandem olefin metathesis in indolizidine scaffolds <2006OL5553>. 

Grubbs reported tandem olefin metathesis/hydrogenation as a means to make satnrated cyclic prodncts and a one-pot RCM/transfer dehydrogenation/hydrogenation ronte to (R)-(-)-Mnscone utilizing (4a) (Scheme 19). Snapper and coworkers took advantage of the isomerization side reaction... 

The molybdenum-alkylidene 9 [130] promoted tandem olefin metathesis-carbonyl olefination of olefinic ketones offers an effective synthetic method for cy-cloalkenes (Scheme 4.56 Table 4.19). The complex 9 initially reacts with the ter-... 

Scheme 4.S6. Formation of cycloalkenes from olefinic ketones by the molybdenum-alkylidene promoted tandem olefin metathesis-carbonyl olefination.

Tab. 4.19. Tandem olefin metathesis-carbonyl olefination promoted by the molybdenum-alkylidene 9.

Tandem carbonyl olefmation—olefm metathesis utilizing the Tebbe reagent or dimethyl-titanocene is employed for the direct conversion of olefmic esters to six- and seven-mem-bered cyclic enol ethers. Titanocene-methylidene initially reacts with the ester carbonyl of 11 to form the vinyl ether 12. The ensuing productive olefm metathesis between titano-cene methylidene and the cis-1,2 -disubstituted double bond in the same molecule produces the alkylidene-titanocene 13. Ring-closing olefin metathesis (RCM) of the latter affords the cyclic vinyl ether 14 (Scheme 14.8) [18]. This sequence of reactions is useful for the construction of the complex cyclic polyether frameworks of maitotoxin [19]. 

Whereas Hegedus [335] and Danishefsky [336] were the first to discover a tandem Heck reaction from o-allyl-A -acryloylanilines leading to tricyclic pyrrolo[l,2-a]indoles or pyridino[l,2-a]indoles [336], it has been the fantastic work of Grigg to unleash the enormous potential of this chemistry. Grigg and his co-workers parlayed their Pd-catalyzed tandem polycyclization-anion capture sequence into a treasure trove of syntheses starting with IV-allyl-o-haloanilines [337-345], Diels-Alder and olefin metathesis reactions can be interwoven into the sequence or can serve as the culmination step, as can a wide variety of nucleophiles. An example of the transformation of 289 to 290 is shown below in which indole is the terminating nucleophile [340],... 

C. A. Chen, P. Hofmann, P. Catalyst Screening by ESI Tandem-MS Hofmann Carbenes for Olefin Metathesis. Chem. -Eur.J. 2001, 7,4621-4632. 

Catalytic metathesis has been accomplished via a tandem combination of catalytic alkane dehydrogenation, olefin metathesis and subsequent olefin hydrogenation (Scheme 12.6). Two factors are crucial for this transformation ... 

More recently, the same principle was applied by the same authors to cyclic alkanes for catalytic ring expansion, contraction and metathesis-polymerization (Scheme 13.24) [44]. By using the tandem dehydrogenation-olefin metathesis system shown in Scheme 13.23, it was possible to achieve a metathesis-cyclooligomerization of COA and cyclodecane (CDA). This afforded cycloalkanes with different carbon numbers, predominantly multiples of the substrate carbon number the major products were dimers, with successively smaller proportions of higher cyclo-oligomers and polymers. 

The molybdenum complex Mo(NAr)(CHCMe2Ph)[(3)-Me2SiBiphen] 43 was used for catalytic asymmetric olefin metathesis reactions such as desymmetrization of trienes, kinetic resolution of allylic ethers, tandem catalytic asymmetric ring-opening metathesis/cross-metathesis. Interestingly, tandem catalytic asymmetric ring-opening... 

Adihart, C., Hinderling, C., Baumann, H., Chen, P. Mechanistic Studies of Olefin Metathesis by Ruthenium Carbene Complexes Using Electrospray Ionization Tandem Mass Spectrometry. J. Am. Chem. Soc. 2000, 122, 8204-8214. 

It has been revealed that the ruthenium carbene complex 6 can promote not only the olefin metathesis but also hydrogenation and isomerization. Louie et al. reported that the one-pot tandem ring-closing... 

A.S. Goldman, A.H. Roy, Z. Ahuja, W. Schinski, M. Brookhart, Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis, Science 2006, 312,... 

Olefin metathesis. Cross metathesis permits a facile access to allylsilanes and Z)-a,P-unsaturated nitriles. Furthermore, employing an alkene metathesis in tandem with asymmetric allylboration provides functionalized alkenes. ... 

Scheme 15. Synthesis of complex polyether frameworks by tandem methylenation/olefin metathesis. (Nicolaou et al., 1996p...

Recently, metathesis of cyclooctane was reported using the tandem system having the pincer-ligated iridium complexes for hydrogenation/dehydrogenation and Schrock-type Mo-alkylidene complexes for olefin metathesis [78]. However,... 

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