Grubbs-catalyzed metathesis

Grubbs-Catalyzed Metathesis of Eugenol with 1,4-Butenediol to Prepare a Natural Product... 

EXPERIMENT 35 Grubbs-Catalyzed Metathesis ofEugenol with l,i-Butenediol to Prepare a Natural Produd 331... 

The main reason for the rapid development of metathesis reactions on a laboratory scale (the reaction itself had been known for quite a long time) has been the development of active and robust second-generation ruthenium catalysts (6/3-14 to 6/3-16), which usually provide better yields than the first-generation Grubbs catalysts (6/3-9 or 6/3-13) (Scheme 6/3.2). This also reflects the huge number of domino processes based on ruthenium-catalyzed metathesis, which is usually followed by a second or even a third metathesis reaction. However, examples also exist where, after a metathesis, a second transition metal-catalyzed transformation or a pericyclic reaction takes place. 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

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. 

Since the definitive experiments of Katz and Grubbs appeared in the literature, the non-pairwise mechanism has become the accepted pathway for metathesis. Subsequent investigations have supported this pathway.1718 Key intermediates in the non-pairwise mechanism are metal-carbene and metallacyclo-butane complexes. Both have been prepared and shown to catalyze metathesis, and more recently both species have actually been observed in the same reaction mixture and shown to interconvert during it, thus offering additional support for Mechanism 3.19 The next section will cover the discovery of discrete metal-carbene complexes that do serve as metathesis catalysts. 

Pheromones are chemicals that are used by animals and plants for communication. Insects utilize pheromones extensively to indicate their availability for reproduction, to sound alarms, and to make known the presence of food. The use of pheromones in small amounts in traps can interfere with the reproduction of harmful insects in an environmentally friendly manner. Recently, Grubbs second-generation catalyst (24) was used to synthesize on an industrial scale the sex attractant pheromone of the peach twig borer, a pest that attacks peach, plum, nectarine, and almond crops.46 Equation 11.16 shows how Ru-catalyzed metathesis of 5-decene and l,10-diacetoxy-5-decene produces a 50% yield of E-Z mixture (the desired E-isomer predominates, and the presence of small amounts of Z-isomer does not lower the activity of the pheromone) of the desired pheromone at low temperature. The unreacted starting materials are recovered by vacuum distillation and recycled. 

BTF can be used for some important transition metal catalyzed reactions, such as the Grubbs olefin-metathesis reaction [64] (11.1), the Petasis olefination [65]... 

Interesting examples of the asynunetric synthesis of P-stereogenic vinylic phospholene boranes 183 using sparteine catalysis and Grubbs catalyzed ringclosing metathesis have been described (Scheme 58) [85]. 

The original ruthenium carbene complexes prepared by Grubbs, Ru-1 and Ru-2, see eqn. (15), have served very well to effect numerous RCM and ROMP reactions. Nevertheless, the race is on to find even better ruthenium complexes that are either more stable or will catalyze metathesis of an even wider range of substrates. Amongst these are 11-14. 

Grubb s-Catalyzed Metathesis of Eugenol with cfs-1,4-Butenediol... 

Different types of olefin metathesis, all proceeding according to the Chauvin mechanism and catalyzed by Schrock-type or Grubbs-type metathesis catalysts. Tandem, domino and cascade metathesis reactions couple several of these reactions (in particular ROMP + ROM). 

Grubbs et al. reported that the ruthenium-catalyzed RCM of a conjugated diene proceeds in such a way that the less hindered olefin moieties participate in the reaction. Consequently, RCM of 115 gives exo-methylene compound 116, and not exo-vinyl compound 117 (Scheme 24) [105]. This regioselectivity is complementary to that observed for enyne metathesis of 118, which gives exclusively 117 (Scheme 24) [106a]. 

Within this chapter, two sections are devoted to rhodium and ruthenium. The two main procedures using rhodium are first, the formation of 1,3-dipoles from diazocompounds followed by a 1,3-dipolar cycloaddition [10] and second, hy-droformylation [11], The ruthenium-catalyzed domino reactions are mostly based on metathesis [12], with the overwhelming use of Grubbs I and Grubbs 11 catalysts. 

For a recent report on the mechanism of the Ru-catalyzed ring-dosing metathesis, see Dias EL, Nguyen ST, Grubbs RH (1997) J Am Chem Soc. 119 3887... 

Polymers Catalytic reactions involving C=C bonds are widely used for the conversion of unsaturated fatty compounds to prepare useful monomers for polymer synthesis. Catalytic C-C coupling reactions of unsaturated fatty compounds have been reviewed by Biermann and Metzger [51]. Metathesis reactions involving unsaturated fatty compounds to prepare co-unsaturated fatty acid esters have been applied by Warwel et al. [52], Ethenolysis of methyl oleate catalyzed by ruthenium carbenes developed by Grubb yields 1-decene and methyl 9-decenoate (Scheme 3.6), which can be very useful to prepare monomers for polyolefins, polyesters, polyethers and polyamide such as Nylon 11. 

Sanford, M. S. Love, J. A. Mechanism of Ruthenium-catalyzed Olefin Metathesis Reactions. In Handbook of Metathesis-, Grubbs, R. H., Ed. Wiley-VCH Weinheim, 2003 Vol. 1, pp 112-131. 

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