Cyclooctane metathesis

Scheme 22 Proposed mechanism for ring expansion and ring contraction with some selected cyclic and macrocyclic alkanes formation from cyclooctane metathesis. ROM ring-opening metathesis, RCM ring-closing metathesis. Iso double-bond isomerization...

Scott and coworkers [60] have also investigated applications of AM to cycloalkanes. They found, for example, that cyclooctane undergoes metathesis by 7 in tandem with 1, 4a, or 6, to give a range of cyclic products, including (surprisingly) cycloheptane, but mostly low cyclooligomers in which the carbon number is a multiple of 8. The proposed mechanism is shown in Scheme 3. 

Because of the excellent performance of the new catalysts, many research groups use ringclosing metathesis as the key step in natural product synthesis [12]-[18]. Scheme 6 shows some examples. Via ring-closing metathesis of the olefin 37 to the hydroazulene 38, Blechert et al. [12] succeeded in synthesizing a cyclic system which is part of many sesquiterpenes. Cyclooctane derivatives, whose synthesis is the main problem in taxol synthesis, can be obtained in good yields (39 40), as demonstrated by Grubbs et al. [ 13]. 

Recently, metathesis of cyclooctane was reported using the tandem system having the pincer-ligated iridium complexes for hydrogenation/dehydrogenation and Schrock-type Mo-alkylidene complexes for olefin metathesis [78]. However,... 

Scheme 21 Proposed mechanism for metathesis of cyclooctane into cyclohexadecane...

Precatalyst 27 has shown surprising results in the metathesis of cyclooctane and cyclodecane with broad distribution of lower and higher macrocyclic alkanes. Cyclopentane, cyclohexane, and cycloheptane were found to be inactive under similar condition [79]. 

The metathesis of cyclic alkanes using this catalyst was studied, where it was found to be able to convert cyclooctane (COA) into a distribution of cyclic (from Cj to Cy) and macrocyclic alkanes with the formula (from C 2 to C )... 

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