Ring-closing metathesis strained compounds

Highly strained cyclic compounds containing an alkyne group can be prepared upon complexation to Co2(CO)6. The success of these reactions relies on the severely bent nature of the alkyne triple bond when complexed to cobalt. Cyclization of (137) to form bicyclo[7.3.0]tridecane (138), a calichiamycinone derivative has been reported (Scheme 204). The nine-membered enyne complex (140) was prepared by ring-closing metathesis of (139) (Scheme 205). A related reaction was used to give complex (141) (Scheme 206). It should be noted that no cyclization occurs without prior complexation to cobalt in the latter case. A complexation-initiated... 

Metathetic ring closure. The powerful technique of ring-closing metathesis (RCM) using ruthenium carbene complexes such as 1 and 2 is shown in the preparation of a highly strained tricyclic compound that cannot be realized using MeReOj. 

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