Cyclo-heptadiene

During an attempt to synthesize a boracycloheptadienylrhodium complex from l-phenyl-4,5-dihydroborepin, LiC(CH3)3, and [Rh(l,5-CgH,2)Cl]2, the 7j-l,5-cyclooctadiene (l-4-Tj-l-phenyl-l-borato-l,3-cyclo-heptadiene)rhodium 39 was obtained (43). Presumably, the unexpected formation of 39 (60%) occurs by addition of a rhodium-hydride compound (formed by elimination of isobutylene from a r-butylrhodium complex) to the 4,5-dihydroborepin. Its constitution is deduced from H- and UB-NMR data. The bora-5,6,7-trihydroborepinyl acts as an allyl ligand and thus contributes three electrons to complex bonding. (See Fig. 9.)... 

Next, other unsaturated carbocyclic systems are discussed, such as dibenzo-cyclo-heptadienes ( atropisomeric biphenyls), dihydropleiadenes, cycloheptatrienes and their benzo-derivatives. Most of these compounds exist in a half-boat or boat conformation. Tropones are considered in the light of recently published work. 

In addition to the representative [3 + 2] cycloaddition reactions shown in Table I, the delocalized singlet vinyl carbenes have been shown to participate as tt2a components of non-Hnear cheletroplc [tt 2S + it 2a] cycloadditions to provided cyclopropanes with an observable endo effect, and asw2s components of [tt4s + i2s] cycloadditions with selected dienes to provide cyclo-heptadienes, (Scheme 1). This thermal reactivity of cyclopropenone ketals... 

The structure of the sex pheromone for the Fucus species, fucoserratene (11), was elucidated in 1973.16 The positions and geometries of alkenes were revealed by comparison of the gas chromatographic behavior with those of the isomeric conjugated 1,3,5- and 2,4,6-octatrienes. To date, a series of hydrocarbons and epoxides 1-11 and their stereoisomers have been identified within the pheromone bouquets of more than 100 different species of brown algae.17-23 Identification of these compounds was based on a combination of gas chromatography-mass spectrometry (GC-MS) analysis and by comparison with authentic synthetic compounds. These sex pheromones were all lipophilic, volatile compounds that consisted of C8 or Cn linear or monocyclic hydrocarbons or their epoxides. The monocyclic compounds have a cyclopropane, cyclopentene, or cyclo-heptadiene structure. Interestingly, the relationships between the chemical structures of pheromones and the taxonomical classifications of algae are unclear (Table 1). 

Diene iron tricarbonyl complexes are prepared by thermal or photochemical reaction of conjugated dienes with iron pen-tacarbonyl in the presence of TMANO, triiron dodecacarbonyl, ()]" -benzylidenacetone)iron tricarbonyl, diiron nonacarbonyl, or diiron nonacarbonyl absorbed on silica gel in the absence of solvent. The latter method is particnlarly usefiil for the preparation of complexes from polar electron-rich dienes and heterodienes. A reductive complexation of cycloheptatrienes using iron tricarbonyl and sodium borohydride to give cyclo-heptadiene iron tricarbonyl has been developed (Scheme 126). 

Such reactions are mueh more efficient for bridged (bicyclic) cyclohexadienes and cyclo-heptadienes. 7,7-Dimethyl-8-methylenebicyclo[2.2.2]octa-2,5-diene (5) affords 6,6-dimethyl-7-methylenetricyclo[3.3.0.0 ]oct-3-ene (6, isolated by preparative GC) regiospecifically, i.e. interaction of the constrained double bonds is preferred to a reaction involving the exocyclic methylene group. 

Ring compounds containing carbon bridges are also formed by addition of, e.g., maleic anhydride to alicyclic dienes such as cyclopentadiene and cyclo-heptadiene of the two possible stereoisomers it is always the erafo-compound that is produced (Woodward-Hoffmann rules38). Such reactions, however, fail when the product would break Bredt s rule. 

For an eight-membered metallacycle as reactive intermediate in the formation of a cyclo-heptadiene, see J. W. Herndon, G. Chatteijee,... 

Exhaustive methylation of a-methyltropidine followed by a Hofmann degradation eliminates the nitrogen as trimethylamine and the low boiling cycloheptatriene (tropilidene) was isolated in good yield (22,121). Tropane may be converted through the intermediate methyltropane to A -cyclo-heptadiene (hydrotropilidene) by a similar process. In the conversion of methyltropane methohydroxide to cycloheptadiene (139), 20% of the methyltropane is reformed by the loss of methanol, a side reaction which occurs in most Hofmann degradations to a greater or lesser extent. Cycloheptatriene and cycloheptadiene have been reduced to cycloheptane (194) which in turn has been oxidized (nitric acid) to pimelic acid. 

Controlled polyfunctionalization of cycloheptene can be achieved via nucleophilic addition and subsequent decomplexation of cyclo-heptadiene molybdenum cationic complexes (Scheme 16). ... 

Allo-ocimene (33) can be cyclized by alkali metal-amine suspensions to cyclo-heptadienes, 1,2,4-trimethylcyclohepta-1,3-diene (81 %), 2,6,6-trimethylcyclohepta-1,3-diene (48%), and 1-ethyl-4-methylcyclohepta-1,3-diene (18%), were obtained using sodium-piperidine, n-butyl-lithium-TMEDA, and sodium-isopropylamine,... 

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