Cross cyclic/acyclic alkene

The ring-opening cross-metathesis reaction is similar to the acyclic cross-metathesis reaction discussed above, except that one of the acyclic alkenes is replaced with a strained cyclic alkene (Scheme 5). 

Optimal yields were obtained by slow addition of the alkene substrates to a solution of the ruthenium vinylalkylidene and this allowed just two equivalents of the acyclic alkene to be used without significant formation of polymeric products. Unlike the acyclic cross-metathesis reactions, which generally favour the formation of tram products, the above ring-opening metathesis reactions yielded products in which the cis stereoisomer is predominant. Particularly noteworthy was the absence of significant amounts of products of type 31, formed from metathesis of one cyclic and two acyclic alkenes. In fact, considering the number of possible ring-opened products that could have been formed, these reactions showed remarkable selectivity (GC yields > 80%). 

Use of a symmetrical acyclic alkene limits the possible metathesis products to the desired diene (for example 45) and products formed from polymerisation of the cyclic substrate. Competing ROMP was suppressed in these reactions by using dilute conditions and a tenfold excess of hex-3-ene. By adding the cyclic substrate slowly to a solution of the catalyst and ris-hex-3-ene (which was significantly more reactive than the trans isomer), less than two equivalents of the acyclic alkene were used without causing a significant drop in the cross-metathesis yield. 

Cross-Metathesis Between a Cyclic and an Acyclic Alkene... 

Olefin metathesis has proven to be useful for the synthesis of an enormous variety of unsaturated compounds, including cyclic, acyclic, and polymeric alkenes. The studies discussed in previous sections focused on fundamental reactivity patterns that apply to all types of metathesis reactions, from cross-metathesis to polymerizations. With many of the basic mechanistic features established, many... 

CROSS METATHESIS BETWEEN CYCLIC AND ACYCLIC ALKENES... 

Metathesis of alkenes has been reviewed in terms of cross-metathesis, ring opening and closing, disproportionation, transmutation, and self-metathesis.34 A review on catalytic processes involving ft -carbon elimination has summarized recent progress on palladium-catalysed C-C bond cleavage in various cyclic and acyclic systems.35... 

The cross-metathesis between an acyclic and a cyclic alkene, nowadays called ring-opening metathesis (ROM), provides a convenient route to certain polyunsaturated compounds. For example, ethenolysis of cycloalkenes yields a,w-dienes (eq. (6)), which may be useful, e. g., as crosslinking agents in polymers and as precursors for a, -difunctional compounds [13],... 

Some examples of cross-metathesis between isotopically labelled alkenes have been given in Chs. 3 and 5. They demonstrate not only the fission of the double bond but also the occurrence of non-productive metathesis. Here we summarize the information on all types of cross-metathesis reaction involving only acyclic compounds. Cross-metathesis between cyclic and acyclic compounds is discussed in Ch, 15. 

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