Diallenes, cyclic

Geminal dibromocyclopropanes have been reduced by chromium(lI) - (-i-)-tartrate complex and by butyllithium - (+)-sparteine complex to give cyclic allenes and 1-phenyl-l,2-butadiene with very low enantioselectivity (< 1 % op)122. In addition, cyclic diallenes of unknown optical purity have been reported123, l24, e.g., 3,4,9,10-cyclododecatetraene-l,7-dione is prepared using a stoichiometric amount of methyllithium and a sixfold excess of (-)-sparteine123,124. 

Although this route to a,cu-diallenes from terminal bisolefmic precursors has often been used in allene hydrocarbon chemistry, the reaction is actually complex and yields product mixtures containing cyclic and bicyclic hydrocarbons when the spacer between the double bond and the allene group is short (between one and three methylene groups), see (a) Th. Miebach, H. Wiister,... 

Bowes, C. M. Montecalvo, D. F. Sondheimer, F. o-Dipropadienylbenzene and 2,3-dipropa-dienylnaphthalene. The oxidation of diallenes to cyclic peroxides with triplet oxygen. Tetrahedron Lett. 1973, 3181-3184. 

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