Bicyclo octa-2,6-diene synthesis

M. Green, J. A. K. Howard, J. L. Spencer, and F. G. A. Stone, Synthesis of Ethylene, Cyclo-octa- 1,5-diene, Bicyclo [2.2.1]heptene, and trans-Cyclo-octene Complexes of Palladium ) and Platinum(O) Crystal and Molecular Structure of Tris(bicyclo2.2.1]hepte-ne)platinum, J. Chem. Soc., Dalton Trans. 1977, 271-277. 

The present two-step procedure for the synthesis of 1,3,5-cyclooctatriene uses commercially available 1,5-cyclooctadienes as starting material. Although allylic bromination of 1,5-cyclooctadiene with N-bromosuccinimide produces a mixture of 3-bromo-1,5-cyclooctadiene and 6-bromo-1,4-cyclooctadiene,2 dehydrobromination of this mixture with UCI-IJ2CO3/DMF affords only 1,3,5-cyclooctatriene, which is in equilibrium with its valence isomer bicyclo[4.2.0]octa-2,4-diene. 

The key intennediate for the synthesis of ( )-sinulaiene (159), a structurally unusual marine natural product, was the bicyclic divinylcyclopropane (160). Successful Cope rearrangement of this substance would be expected to proceed via the endo isomer (161) to produce the bicyclo[3.2.1]octa-2,6-diene (162), possessing the correct stereochemistry at C-4 (exo-isopropyl group) and fimctionality (exo-vinyl group at C-8, enol ether associated with C-6 and C-7) that would allow the straightforward preparation of the tricyclic ring system of ( )-(159). 

Upon decomplexation, using various methods, cyclopropane products are obtained (see Section 5.2.6.1.1). As an example, synthesis of homotropone (9 bicyclo[5.1.0]octa-3,5-dien-2-one) is achieved starting from cyclooctatetraenetricarbonyliron complex via protonation, formation of the bicylo[5.1.0]octadienylium cation complex 8, nucleophilic addition of sodium hydroxide and oxidative decomplexation. ... 

The synthesis of bicyclo[3.2.l]octa-2,6-diene derivatives with functionality at a bridgehead position is achieved by the reaction pathway 134 -> 135 - 136 - 137888. 

Table 1. Diastereoselective Synthesis of Bicyclo[3.2.1]octa-2 6-dienes...

The addition of various carbon and heteroatom nucleophiles to (bicyclo[5.1.0]-octadienyl)iron cations has been reported. Mostly, the nucleophile attacks at the terminus of the dienyl system to form substituted (bicyclo[5.1.0]octa-2,4-diene)iron complexes. The nucleophile stereoselectively attacks from the rear side of the dienyl system, opposite to the iron atom. The method can be used for the synthesis of cis-2-(2 -carboxycyclopropyl)glycine (CCG-III) (Scheme 4-180). ... 

Freeman, P.K. and Kupar, D.G., Synthesis of bicyclo[3.2.1]-octa-3, 6-dien-2-one. An unusual valence isomerization, Chem. Ind. (London), 424,1965. 

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