DIASTEREOSELECTIVE SYNTHESIS OF CYCLODODECA-1,6-DIALLENES (=CYCLODODECA-1,2,6,7-TETRAENES)

The synthesis of substituted cyclododeca-1,6-diallenes (= cyclododeca- 1,2,6,7-tetraenes) from cyclododeca-5,11-diyne-1,4-diols is described (Schemes 1 and 3). The ca. 1:1 mixtures of the stereoisomers of the cy clododeca-1,6-diallenes were formed in high yields from the ca. 1:1 di astereoisomer mixtures of the 1,4-disubstituted cyclododeca-5,11-diyne s by reactions with Me(2)CuLi or t-BuMgCl/(CuI)-I-1. In mechanisticall y relevant experiments with the pure diastereoisomers of 1,4-dimethylc yclododeca-5,11-diyne-1,4-diol, it is demonstrated that the configurat ion is conserved in these reactions. The first synthesis of a 1-substi tuted cyclododeca-2,8-diyne bearing only one propargylic leaving group gives access to a mixed 12-membered allen-yne (Scheme 5).