Diolefins metathesis

Several fundamental types of metathesis reactions for monoolefins or diolefins are shown in Eqs. 2-5. 

A general method for the preparation of carbasugars with various ring size consists of the metathesis of properly prepared sugar diolefins. 

A novel approach to enantiopure spirocyclic (3-lactams has been developed by Alcaide et al. [106] using different intramolecular metal catalyzed cyclization reactions with monocyclic unsaturated alcohols 142 (Scheme 35). Ring-closing metathesis is one of the most powerful and reliable methods to construct a ring system. Transformation of alcohols in diolefin precursors followed by ring-closing... 

Among cyclic polyenes, cyclic dienes, trienes and tetraenes have been ring-open polymerised via the metathesis reaction. Representative of the cyclodienes most commonly used for polymerisation are 1,5-cyclooctadiene, norbornadiene (bicyclo[2.2.1]hept-2,5-diene) and dicyclopentadiene as mono-, bi- and tricyclic diolefins respectively. Cycloocta-1,5-diene metathesis polymerisation is another approach to the preparation of 1,4-polybutadiene ... 

Application of the ring-closing olefin metathesis reaction (RCM) for the preparation of car-bocyclic rings from the appropriately functionalized sugars is now well documented [81]. Recently it was applied for the synthesis of compound 122, which can be regarded as a (n,m)-anhydrosugar [81]. The intermediate diolefin 121 was prepared in a few standard steps from the corresponding dialdose 120 (O Fig. 28) [82]. 

An example of the second category is the cross metathesis of cyclooctene and ethylene giving 1, 9-decadiene (60) in about 75% yield (Eqn. 22.55). 42 This reaction between cyclic olefins and ethylene provids an excellent method for the preparation of a, -diolefins. 2 ... 

Terminal dienes (also called a,w-diolefins) are useful in ADMET polymerization. The scheme below shows a number of processes that were patented by Shell Oil Company and were designed to produce terminal dienes. The name FEAST (Further Exploitation of Advanced Shell Technology) was coined to describe these reactions, most of which involve metathesis. Assume that the catalyst is a generic carbene complex, L M=CRR. Propose mechanisms for the transformations indicated by an asterisk near the reaction arrow. 

Different types of monoolefin and diolefin undergo metathesis via contact with a suitable catalyst, resulting in a wide variety of possible products (Eqs 2-5) [1]. 

The i-oleftns obtained have a purity of more than 95 molar per cent of terminal olefins and are devoid of branched structures or diolefinic or cyclic impurities. These z-olefms, which all have an even number of carbon atoms, are produced with yields that vary according to a statistical distribution, with a maximum of C, 0-C, 2-Cj, for example, if the final product is intended for the manufacture of linear alkylbenzene. Due to the low yield of a given cut, it is understandable that the upgrading of all the other fractions is economically necessary. Since the upgrading of the light and heavy fractions is often a problem. Shell in the United States has developed the SHOP (Shell Higher Olefin Process), in which these effluents are converted to a cut for detergents by isomerization and metathesis. 

G. C. Ray and D. L. Crain used the scheme to postulate that metathesis reactions could be extended to the cleavage of cyclic olefins with ethylene to yield alpha-omega diolefins (Figure 6), The four-center scheme implies that in theory the number of metathesis reactions is limited only by the number of compounds containing carbon-carbon multitype bonds. 

Technology for a number of applications of olefin metathesis has been developed (, fO At Phillips, potential processes for producing isoamylenes for polyisoprene synthesis and long-chain linear olefins from propylene have been through pilot plant development. In the area of specialty petrochemicals, potential industrial applications include the preparation of numerous olefins and diolefins. High selectivities can be achieved by selection of catalyst and process conditions. The development of new classes of catalysts allows the metathesis of certain functional olefins (, 14). The metathesis of alkynes is also feasible (15) ... 

Metathesis of mono- and diolefins can be performed with both homogeneous and heterogeneous catalysis. The most important processes involving metathesis steps, the SHOP process and the Phillips triolefin process, are based on heterogeneous catalysts. Homogeneous catalysts are used in the ring opening metathesis of norbor-nene (Norsorex, CDF-Chemie) and cyclooctene (Vestenamer, Hills) [7]. 

This process allows the synthesis of a,co-diolefins by cross-metathesis of cycloolefins with ethylene. The reaction was first studied by Phillips who produced multi-tons of... 

The monomer 7-methylnorbornadiene (7-MeNBD) also undergoes polymerization in the presence of several conventional metathesis catalysts to form poly(7-MeNBD). It is noteworthy that the catalyst OSCI3 (in 1 1 EtOH/PhCl) leads to polymer stereochemistry that is significantly different from that of poly(fl fi-7-MeNB). The OsC -derived polymer of the monoolefin contains predominantly atactic trans olefin structures, whereas the analogous diolefin polymer is composed of nearly exclusively cis alkene structures (97%) and predominantly syndiotactic dyads (r m = 75 25 through the NMR signals of the methyl substituent at 8 16.2-17.0 ppm)." The catalysts Reds... 

Recently, Malcolm Green has proposed the application to olefin polymerization of the mechanism developed for olefin metathesis reactions (Fig. 22) it is an attractive suggestion, and it might represent the actual mechanism in some particular chain addition processes studied recently. It seems, however, very difficult to apply to classical Ti-based Z.N. heterogeneous catalysts, for a number of reasons (odd Ti intermediate oxidation states, unexplained stereocontrol features, non-relevance for diolefins, etc.). 

In addition to some problems raised by the many molecular motions in the complex for every propagation step, this mechanism would irrply in the case of diolefins unlikely situations from a steric point of view. Although this pathway is probably valid for reactions related to olefins metathesis processes, it necessitates fxirther experimental evidence to be applied to olefins and diolefins usual coordination polymerizations. 

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