Ruthenium-catalyzed cross-metathesis

The functionalization of SAMs via ruthenium-catalyzed cross metathesis of vinyl-terminated SAMs has been reported by Lee et al.76 to install a variety of acrylic derivatives on SAMs bearing vinyl groups on their outer surface. The major drawback of this approach is the intra-SAM metathesis which causes the formation of a mixture of surface-bound products, limiting the reproducibility of the method. The formation of urethanes by the reaction of diisocyanates77 or isothiocyanates78 with hydroxyl- and amino-terminated SAMs has been reported as well. The reaction of hydroxyl-terminated SAMs with diisocyanates, allowed the preparation of isocyanate SAMs that proved to be reactive towards amines, alcohols, and water, displaying the standard chemistry of the isocyanate groups.77... 

Treatment of 1,2-diamino substrates with 1,2-dicarbonyls for the formation of the pyrazine core was a commonly used approach in 2013. Schmidt and his group developed a one-pot synthesis of quinoxahnes, involving a ruthenium-catalyzed cross-metathesis reaction of the starting styrene, forming the respective stilbene, followed by a ruthenium-catalyzed oxidation to the 1,2-diketone, and a subsequent condensation with phenyl-ene diamine, yielding the respective diarylquinoxalines 128 in moderate yields (Scheme 55) (13JOC5427). 

Ferr6-Filmon, K., Delaude, L., Demonceau, A., Noels, A.F., Stereoselective synthesis of (E)-hydroxystilbenoids by ruthenium-catalyzed cross-metathesis, Eur. J. Org. Chem. 2005, 3319-3325. 

Notably, allylboronates can also be successfully used in a ruthenium-catalyzed cross-metathesis/aUyboration sequence for the synthesis of homoaUylic alcohols [109,110]. Likewise, an unsaturated boronic ester annulation strategy with allylic and propargylic alcohols have found very elegant and useful applications in diversity-oriented organic synthesis (Scheme 9.53) [111]. 

Bent ansa-metallocenes of early transition metals (especially Ti, Zr, Hf) have attracted considerable interest due to their catalytic activity in the polymerization of a-olefins. Ruthenium-catalyzed olefin metathesis has been used to connect two Cp substituents coordinated to the same metal [120c, 121a] by RCM or to connect two bent metallocenes by cross metathesis [121b]. A remarkable influence of the catalyst on E/Z selectivity was described for the latter case while first-generation catalyst 9 yields a 1 1 mixture of E- and Z-dimer 127, -127 is the only product formed with 56d (Eq. 19). 

The synthesis and olefin metathesis activity in protic solvents of a phosphine-free ruthenium alkylidene bound to a hydrophilic solid support have been reported. This heterogeneous catalyst promotes relatively efficient ring-closing and cross-metathesis reactions in both methanol and water.200 The catalyst-catalyzed cross-metathesis of allyl alcohol in D20 gave 80% HOCH2CH=CHCH2OH. 

With the bicyclic core (58) in hand, different compounds could be synthesized from the same penultimate intermediate, allowing for late-stage diversification. Different co-side chains were installed via ruthenium(II)-catalyzed cross metathesis using different alkenes (Scheme 12). Since this type of reaction was previously reported in a very similar structure by Sheddan and Mulzer, we were confident that the reactions would be successful. 

Mori M, Tonogaki K, Nishiguchi N. Syntheses of anolignans A and B using ruthenium-catalyzed cross-enyne metathesis. J. Org. Chem. 2002 67 224- 226. 

The cross metathesis of vinylsilanes is catalyzed by the first-generation ruthenium catalyst 9. This transformation has been extensively investigated from both preparative and mechanistic points of view by Marciniec et al. [86]. Interestingly, the same vinylsilanes obtained from cross metathesis may also result from a ruthenium-hydride-catalyzed silylative coupling and there might be some interference of metathesis and nonmetathesis mechanisms [87]. 

The significant potential of the ruthenium complex 65 was further underlined in the catalytic asymmetric ring-opening/cross metathesis of the cyclic alkene 70 (Scheme 44). This transformation is catalyzed by 5% mol of 65 at room temperature, in air, and with undistilled and nondegassed THF to deliver the corresponding diene 71 in 96% ee and 66% isolated yield. In standard conditions (distilled and degassed THF), the alkene 70 reacts in 75 min to give the diene in 95% ee and 76% yield, with only 0.5 mol % of catalyst. 

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

For a review of asymmetric Mo-catalyzed metathesis, see Catalytic Asymmetric Olefin Metathesis, A. H. Hoveyda, R. R. ScHROCK, Chem. Eur. J. 2001, 7, 945-950 for reports on chiral Ru-based complexes, see (b) Enantioselective Ruthenium-Catalyzed Ring-Qosing Metathesis, T.J. Sei-DERS, D.W. Ward, R.H. Grubbs, Org. Lett. 2001, 3, 3225-3228 (c) A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis In Air, J. J. Van Veldhuizen, S. B. 

Strained rings may be opened by a ruthenium carbene-catalyzed reaction with a second alkene following the mechanism of the Cross Metathesis. The driving force is the relief of ring strain. As the products contain terminal vinyl groups, further reactions of the Cross Metathesis variety may occur. Therefore, the reaction conditions must be optimized to favour the desired product. 

A ruthenium-catalyzed ring opening cross-metathesis of 8-oxabicyclo[3.2.1]oct-6-en-3-one 1049 with alkenes provides an efficient method for the preparation of substituted tetrahydropyran-4-ones 1050 (Equation 408, Table 50) <1999X8169, 20010L4275>. Similarly, ozone can be used to cleave the same ring system during the synthesis of chiral tetrahydropyran-4-ones <2006T257>. 

A palladium-catalyzed intramolecular benzannulation of bis-enynes 1135 proceeds chemoselectively to afford dihydroisocoumarins 1136 (Equation 441) <2002JOC2653>. A reaction sequence involving ruthenium-catalyzed yne-ene cross-metathesis of a polystyrene supported undecynoic acid ester followed by a Diels-Alder cycloaddition reaction with DMAD provides the basis for a combinatorial approach to dihydroisocoumarins featuring a variety of side chains at C-6 and C-8 <1999SL1879>. 

Ruthenium-catalyzed olefin cross-metathesis (ring-closing metathesis, RGM) between terminal alkenes and vinyl-boronic acid or esters has recently been developed for the synthesis of ( )-l-alkenylboron compounds from alkenes.459,460 The efficiency of protocol was proved in the synthesis of a key intermediate of epothilone 490 292 461 (Equation (84)). The vinyl boronate was given almost exclusively the trans-adduct. 

The ruthenium-catalyzed olefin cross-metathesis to the preparation of functionalized allyl boronates has resulted in a one-pot three-component coupling procedure for the synthesis of functionalized homoallylic alcohols.617,618 The utility of the protocol was demonstrated in asymmetric allylboration using a tartrate ester (Equation (152)).617... 

Schmidt B. Ruthenium-catalyzed cyclizations more than just olefin metathesis Angew. Chem. Int. Ed. 2003 42 4996-4999. Vemall AJ, Abell AD. Cross metathesis of nitrogen-containing systems. Aldrichim. Acta 2003 36 93-105. 

The two reactions catalyzed by ruthenium complexes, i.e. silylative coupling (SC) (trans-silylation) catalyzed by I, II, V, and VI and cross-metathesis (CM) (catalysts III and IV) of vinyl- and allyl-substituted hetero(N,S,B)organic compounds with commercially available vinyltrisubstituted silanes, siloxanes, and silsesquioxanes provide a universal route toward the synthesis of well-defmed molecular compounds with vinylsilicon functionality. 

Studies of this kind fall broadly into two groups as indicated in Table 15.1. Those labelled P are mainly concerned with the effect of small quantities of acyclic olefin M2 on the MW, yield, and cis content of the polymer produced from the cyclic olefin Mi in this case the ratio [M2]/[Mi] is usually 0-0.05. Those labelled T involve the use of much higher proportions of M2 (with [M2]/[Mi] 0.5-2), with the object of producing telomers with well-defined end-groups, in some cases for synthetic purposes. For example, highly substituted cyclopentane and tetrahydro-fiiran derivatives can be readily made by the cross-metathesis of substituted norbomenes or 7-oxanorbomenes with hex-3-ene or l,4-dimethoxybut-2-ene catalyzed by ruthenium carbene complexes (Schneider, M.F. 1996). If the acyclic olefin is unsymmetrical and represented by Q Q, where Q and are the alkylidene moieties, three series of telomers may be produced, Q (Mi) Q, Q (Mi) Q, Q (Mi) Q, where ti is the number of Mi units. The lowest members of the series (n= 1) are dienes, and it is sometimes possible to deteet, separate, and identify the cc, ct, and tt isomers. 

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