Involvement of three-membered ring compounds in metathesis reactions

4 Involvement of three-membered ring compounds in metathesis reactions 

Cyclopropanes and oxiranes can play an important role in initiation of olefin metathesis reactions via the formation of four-membered metallacycles and their subsequent cleavage sequences (13a, 13b). Conversely, the reverse of such reactions may sometimes be responsible for terminating a metathesis chain reaction. 

An example of this type of forward reaction has already been given in Seheme 2.4. Further examples are provided by (i) the use of norbomene epoxide with W-based catalysts to enhance the ROMP of norbomene derivatives (Devine 1982) (ii) the use of oxygen with norbomene in Ru-based systems to generate such an epoxide (Ivin 1981b) (iii) the use of cyclopropane derivatives with Re207/Al203 (Anisimov 1991) see Ch. 2. 

Metal carbene complexes bearing an alkenyl substituent can also undergo an internal cyclopropanation reaction to yield a bicyclo[ . 1.0] compound (Parlier 1987). 

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