Standard ring-closing metathesis

The following example, adapted from Grubbs original report on ring-closing metathesis is still considered the standard for most ring-closing metathesis reactions. 

All but one of the routes in this class assembled the piperidine moiety of the indolizidine ring system by ring-closing metathesis. Two very similar approaches began with (R,R)-(+)-tartaric acid (287), which was readily converted into the N-allylimide (+)-288 by standard methods (Scheme 40). 

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]. 

Applications of the water-soluble catalysts to initiate methathesis of less strained alkenes are limited by the instability of some of the alkylidenes in water. For example, diethyldiallylmalonate, a standard metathesis substrate in organic solvents, does not ring close in either methanol or water/methanol mixtures. In this case the chain carrying species is the ruthenium methylene complex. As seen above, this complex is unstable in water. However, when the reaction is redesigned to use substrate 17 so that the methylene is not the chain carrying intermediate, ring closing can be carried out under aqueous conditions (Eq. 12). 

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