Dienes ring-closing metathesis

Treatment of enynes 35 and 36 with first generation Grubbs carbene under the above diene ring-closing metathesis conditions did not furnish the desired spiro-cycles. Next, trials of cyclization were attempted by using its imidazolidinylidene... 

Nunez-Zarur F, Solans-Monfort X, Pleixats R, Rodnguez-Santiago L, Sodupe M. DPT Study on the Recovery of Hoveyda-Grubbs-Type Catalyst Precursors in Enyne and Diene Ring-Closing Metathesis. Chem Eur J. 2013 19(43) 14553-14565. 

Pandian S, HiUier IH, Vincent MA, et al. Prediction of ring formation efficiency via diene ring closing metathesis (RCM) reactions using the M06 density functional. 

With a conjugated diene, ring-closing metathesis (RCM) is often possible, particularly where the product ring is unstrained (Eq. 12.5). The reverse of... 

If the reactant is a diene, ring-closing metathesis can occur. 

As stated above, olefin metathesis is in principle reversible, because all steps of the catalytic cycle are reversible. In preparatively useful transformations, the equilibrium is shifted to one side. This is most commonly achieved by removal of a volatile alkene, mostly ethene, from the reaction mixture. An obvious and well-established way to classify olefin metathesis reactions is depicted in Scheme 2. Depending on the structure of the olefin, metathesis may occur either inter- or intramolecularly. Intermolecular metathesis of two alkenes is called cross metathesis (CM) (if the two alkenes are identical, as in the case of the Phillips triolefin process, the term self metathesis is sometimes used). The intermolecular metathesis of an a,co-diene leads to polymeric structures and ethene this mode of metathesis is called acyclic diene metathesis (ADMET). Intramolecular metathesis of these substrates gives cycloalkenes and ethene (ring-closing metathesis, RCM) the reverse reaction is the cleavage of a cyclo-... 

Alkyne cross metathesis Acyclic diene metathesis Asymmetric ring-closing metathesis Asymmetric ring-opening metathesis Cross metathesis... 

The diene core does not necessarily need to remain intact, but can rather be cleaved to enable further functionalization. Taking advantage of the diastereomeric s vitch , such a strategy was implemented together with a ring closing metathesis step in the total synthesis of undecenolides like cladospolide [258,259]. 

The role of complexes 23-28 as catalyst precursors in the ring closing metathesis reactions was investigated. Three different diene substrates diethyldiallyl-malonate (29), diallyltosylamine (30). and dielhyldi(2-methylallyl)malonate (31) were added to the NMR tubes containing a solution of 5 mol% of catalyst precursor in an appropriate deuterated solvent. The NMR tubes were then kept at the temperatures reported in Table X. Product formation and diene disappearance were monitored by integrating the allylic methylene peaks in the H NMR spectra and the results are presented in Table X and the catalytic transformations are depicted in Scheme 3. 

Until now, the most efficient approach to synthesize Freidinger lactams 147 started from a resin-bound cinnamylamine 144. A Fukuyama-Mitsunobu reaction to 145 followed by sulfonamide cleavage and a consecutive appropriate acylation built up the diene 146, which underwent ring-closing metathesis involving Grubb s catalyst 123 to generate the desired lactams 147 (Scheme 27, Table 5) [35d]. 

Scheme 6/3.23. Ring-closing metathesis of diene-ynes 6/3-78 in refluxing CH2CI2.

As part of the development of an efficient synthetic strategy for the synthesis of the little known 3,5- and 3,6-disubstituted tetrahydro-li/-azepines, ring-closing metathesis of the diene 31 to 32 in high yield was reported <06JOM5406>. 

Ring-closing metathesis has been used effectively to prepare the pyrido[3,2-h oxepine derivative 71 in good yield from the pyridyl diene precursor 70 <06TL6235>. 

The oxepine-fused beta-carboline 73 was synthesized in good yield (71%) from the diene precursor 72 using ring-closing metathesis and Grubbs I catalyst <06TL6895>. 

Ring-closing metathesis on the dienes 116 and 117 with Grubbs ruthenium catalyst II 18 afforded the 7-membered ring sulfones 118 and 119 respectively. The diene precursor 116 was accessed from reaction of the sulfonyl chloride 115 with 3-buten-l-ol 114 <06T9017>. 

To effect traceless reactions on a support, as, e.g., exemplified by the ring closing metathesis reactions of bound dienes which concomittantly release the products... 

Ring-closing metathesis (RCM) is an extremely powerful method for transforming acyclic dienes into unsaturated cyclic systems [1], The process is believed to proceed via the catalytic cycle outlined in Scheme 1, and the principal driving force for the reaction is the gain in entropy resulting from the loss of ethene. 

Catalytic ring-closing metathesis makes available a wide range of cyclic alkenes, thus rendering a number of stereoselective olefin functionalizations practical. The availability of effective metathesis catalysts has also spawned the development of a variety of methods that prepare specially-outfitted diene substrates that can undergo catalytic ring closure. The new metathesis catalysts have already played a pivotal role in a number of enantioselective total syntheses. 

Ring-closing metathesis of diene 318 with a Grubbs second-generation catalyst gave 2,5-dihydropyrrole 319 (Equation 56). The absolute stereochemistry was assigned based on single crystal X-ray diffraction analysis... 

The reactions of dienes and other polyenes can be broadly classified as either addition reactions, coupling (or substitution reactions) or rearrangements (including metathesis reactions). This chapter will present recent examples from the literature of synthetic transformations involving polyenes. Cycloaddition and ring closing metathesis reactions appeared in volume one of this series and therefore will not be covered in this chapter. Citations for more detailed descriptions of the individual reactions discussed in this chapter and for more comprehensive reviews appear in the text. 

Fig. 3.50. The mechanism of ring-closing metathesis of dienes and enynes.

Homogeneous Catalysis through Heterogeneous Ru Carbenes 471 Tab. 11.1 Ring-closing metathesis of acyclic dienes by Ru complex (10). ... 

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