Large-ring acetylenes synthesis

In the second approach shown in Scheme 10, the vinyl radical was generated by addition of a tributyltin radical to the terminal acetylene group. In this case, the allyl radical formed in the first cyclization reaction might provide a large steric bias during the second ring closure and could thus impose a better stereoselectivity than in the first approach. The synthesis commenced from the same starting material 77 as in the synthesis of 78. The butenyl chain was attached first and the butynyl chain was introduced second to provide ketoester 83. 

This chapter presents a selective account of new developments in the chemistry of acetylenes since the appearance of previous reviews in this series Three outstanding features of recent acetylene chemistry are the use of metal derivatives, the synthesis of large carbon rings containing several triple bonds and studies in the field of enediyne anti-cancer antibiotics, e.g. Dynemicin A(l), which were discovered only six years ago . ... 

Figure 14 Template synthesis of multiring catenanes. The coordination fragments are drawn in thick lines and the triangles represent the terminal acetylenic functions. The systems obtained are made of w +1 peripheral rings interlocked to a large central ring resulting from a cyclooligomerization process.

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