Olefins enyne ring closing metathesis

Enynes containing a cycloalkene moiety can lead, in the presence of another olefin and a catalytic amount of ruthenium carbene complex, to ringopening and ring-closing metathesis (ROM-RCM) followed by cross metathesis (CM) to produce trienes (Scheme 7). 

The synthesis of heterocycles via the olefin metathesis reaction (RCM, ring closing metathesis, section 2) and via the cycloisomerization of dienes, diynes, and enynes (section 3) belongs to category 1... 

More complex small molecules can also be made by metathesis cascades and tandem reaction sequences involving olehn metathesis components [41], The examples illustrated in Fig. 4.13 include inter- and intramolecular enyne metathesis between an olefin and an alkyne [42], ring-opening cross metathesis to form new substituted acyclic olefins [43], ring-opening ring-closing sequences... 

There is only one example in the literature where an enyne RCM coupled to an intermolecular CM in a sequence process has been applied in the synthesis of a natural product. The synthesis of (-i-)-8-epi-xanthatin, isolated from the leaves extracts from Xanthium canadense, was proposed by Martin et al. through an enyne RCM-CM cascade combining ring closing of 8 with a CM with 9 [13]. The special challenge for this transformation consists in the use of an electron-poor olefin for the final metathesis reaction. The use of [Ruj-III (20mol%), the catalyst of choice for this type of transformations [14], and an excess (10 equiv.) of the methyl vinyl ketone 9 resulted in the formation of the desired product in 83% yield (Scheme 11.3). 

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