Cleavage 1,3-diene central bond

Ring opening by reductive cleavage of 1,3-diene central bonds... 

Simpler bicyclobutanes can also be converted to dienes, but in this case the products usually result from cleavage of the central bond and one of the edge... 

The Hiickel-aromatic dipotassium cyclooctatetraenediide is formed by spontaneous cleavage of the central bond in bicyclo[3.3.0]octa-3,7-diene-2,6-diyldipotas-sium (387, Scheme 1-302). " The bicyclic allylpotassium 388 (Scheme 1-302) equally gets rid of ring strain by scission of the central carbon-carbon bond. Accidental protonation by the solvent gives a mixture of regioisomeric dienes. 

The reaction of 2,3-diaryl(tetrasilyl)tetrasila-1,3-diene 65 with t-BuLi gives the corresponding l,l-disilyl(aryl)lithiodisilene 69 in 67% yield as orange crystals [Eq. (10)].21 The formation of lithiodisilene 69 is explained by a single-electron transfer followed by cleavage of the central Si-Si bond. 

The mobile Jt-electrons of unsaturated systems, responsible for the stabilization of the carbocations, provide equally efficient stabilization for carbanions. Consequently, a retrosynthetic cleavage of a benzylic, allylic, or propargylic C-C bond has additional merits since the resulting fragments can be visualized as either an electrophile or a nucleophile. The dual synthetic value of the allylic moiety has been extensively utilized in the synthesis of a large number of natural acyclic isoprenoids. The structures of many of these compounds look like they were purposely tailored for this type of retrosynthetic analysis. In fact, the 1,5-diene system, usually present in their structure (Scheme 2.19), immediately suggests the cleavage of its central C-3-C-4 bond, which leads to two allylic precursors. 

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