Stereoselective Synthesis of - and Z -Silylated Endiynes

Synthesis of 5-Methylene-1,3-Cyclohexadienes (o-lsotoluenes) and 1,2,4,6-Heptatetraenes (Diene-Allenes) 

To promote Peterson olefination, the use of KH results in the formation of o-isotoluene derivatives [2d, 7], On the other hand, treatment of allenic alcohols with concentrated sulfuric acid produces the diene-allenes. The preference for Z geometry of the methyl-substituted a C=C in silylated allenic alcohol is attributed to the allylic methyl group at the C-1 position, favoring the axial position in the chair-like transition state, thus avoiding the severe steric interaction between the equatorial allylic methyl and the equatorial rigid bicyclic ligand on the boron. 

Synthesis of Enyne-Allenes, Dienyne-Allenes, and Trienyne-Allenes, and Their Cycloisomerization 

The endiyne and enyne-allene have attracted the attention, as they undergo facile cycloaromatization to produce reactive biradicals [1], which could mimic the DNA-cleaving mechanism and properties of the new class of very potent antitumor antibiotics calicheamicins [2], esperamicins [3], neocarzinostatin [4], and dynemicins [5]. 

9-Allenyls-9-BBN required for the synthesis of these unsaturated compounds are obtained by the following reaction sequence. Allenylsilanes [6] are lithi-ated with tert-butyllithium [7], followed by treatment with B-OMe-9-BBN and 

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