Hepta-1,6-dienes

Biradical I would yield cyclopentene plus ethylene, biradical II the hepta-1,6-diene. Process I may have a lower energy of activation because of the stabilization of the free electron by the secondary carbon atom and also because less energy is required to compress the appropriate carbon-carbon bond, in the cyclopentane ring to yield the cyclopentene, than to rupture the ring to give the diene. 

At the temperatures where the decomposition of this bicyclic compound occurs at a reasonable rate there is some decomposition of the primary products. Cyclopentene decomposes by a molecular path to yield cyclopentadiene plus hydrogen. This decomposition has been studied in detail by Vanus and Walters (1948). The decomposition of the hepta-1,6-diene is also important and appears to be predominantly a non-chain homogeneous process, and may occur by the cyclic transition state shown below ... 

Grigg et al. also introduced another Heck-type reaction. 2,6-Dibromo-hepta-1,6-dienes 80 cyclize to the same products 83 (n = 5) as do 2-bromo-1,6-dienes 78 (n = 5) when treated with the usual precatalyst mixture, yet containing a stoichiometric amount of triphenylphosphine [63,64], In this case, palladium dibromide rather than hydridopalladium bromide is eliminated in the final step of the cross-coupling reaction, and the palladium(II) salt is reduced by the phosphine to regenerate the reactive palladium(O) species. Completely selective exo-trig cyclizations occur in these examples, however, the respective cyclohexane derivatives with n = 6 are formed in poor yields. Additionally, it is sometimes difficult to separate the product from the phosphine oxide after aqueous work-up. This latter difficulty was circum-... 

The decomposition of this compound occurs between 426 and 464° C by two concurrent paths to yield as initial products cyclopentene plus ethylene and hepta-1,6-diene. 

Scheme 11.1 Mechanism accounting for chain transfer with hepta-1,6-diene in the ROMP of cyclopentene catalyzed by WF6/EtAlCl2 to give high-ds polymer (Ofstead 1980).

A cycloheptatrienide trianion would have ten ir-electrons and thus might be a stablised (4n+2) electron system. There is evidence for its formation in solution, when either hepta-1,3,6-triene or, more surprisingly, hepta-1,6-diene is treated with n-butyl lithium in tetramethylethylenediamine [390]. The lithium salt is apparently solvated by the amine. Its and n.m.r. spectra show singlets at 6 4.55 and 66.0, respectively. It reacts with deuterium oxide to give a mixture of trideuteriocycloheptadienes and with ethyl sulphate to give a mixture of triethylcycloheptadienes. 

Synonyms Allyl ionone CetoneV 1,6-Heptadien-3-one 1-(2,6,6-Trimethyl-2-cyclohexene-1 -yl)-1,6-heptadiene-3-one 1 -(2,6,6-Trimethyl-2-cyclohexenyl) hepta-1,6-dien-3-one Empirical C16H24O... 

Irradiation of cycloheptene in the presence of mercury gave a mixture of norcarane, vinylcyclopentane, hepta-1,6-diene, and other minor products. Deuterium labelling showed that the norcarane arose via a 1,2-hydrogen shift followed by ring-closure. The photochemical conrotatory ring-closure of all possible 1,3-dimethyl- and 1,4-dimethyl-cyclohepta-1,3-dienes has been carried out. " ( )-Grandisol has been synthesized from eucarvone, the first step in the synthesis being the photoisomerization of eucarvone to l,4,4-trimethylbicyclo[3,2,0]hept-6-en-2-one. °... 

Full details have been published on the hydroboration of acyclic oteo-dienes, using monochloroborane etherate, and on the conversion of the cyclic boranes so obtained into carbocycles. Thus hexa-1,5-diene was treated with monochloroborane to give a mixture of chlorodialkylboranes which were thermally depolymerized and treated with methanol (Cl - OMe) and dichloromethyl methyl ether to give a mixture of cycloheptanone and 2-methylcyclohexanone (74% total yield) in a 90.5 9.5 ratio, respectively. 2,5-Dimethylhexa-1,5-diene was similarly converted into 3,6-dimethyl-cycloheptanone. ° Hepta-1,6-diene has been converted into cycloheptane (67%) by treatment with diborane and then alkaline AgNOj in a new cyclization procedure. Diketones (35 n = 1, 2, or 3) cyclize to give acylcyclopentenes rather than cyclo-heptenones. ... 

Treatment of hepta-1,6-diene with monochloroborane gives a mixture, which was thermally depolymerized and treated with methanol and dichloromethyl methyl ether to give a mixture of cyclo-octanone (major component), 2-methylcycloheptan-one, and 2-ethylcyclohexanone (total yield was 70 %). ... 

Dienes with non-conjugated double bonds, for example, hepta 1,6-diene, do not give products of 1,4-addition in reactions with NO ... 

This type of reaction can also be catalyzed by Pd complexes. Thus, e. g. hepta-1,6-diene afforded 5-ethyl-2-methyl-cyclopent-2-enone and 2-ethyl-5-methyl-cyclopent-2-enone in 16% yield when reacted with CO at 200 °C and 1000 atm in the presence of a 2% solution of diiodo-bis-(tributylphos-phine) palladium (II) [818]. 

Piperidines and Related Compounds.—A simple synthesis of substituted N-arylpiperidines from hepta-1,6-diene is available (Scheme 83). ... 

A synthesis of partially-fluorinated cyclopentanecarboxylic acids based on the cyclization of hepta-1,6-dienes by perfluoroalkyl radicals generated from iodides has been developed (e.g. see Scheme 2) and 1 1 perfluoroalkyl iodide-olefin adducts of the type RpCHg-CHI-CHj CHXY [Rp = perfluoroalkyl X,Y = COgH, CX)2R, CX)R, or CN (R = alkyl)] have proved to be convenient sources of perfluoroalkylated cyclopropanes (e.g. see Scheme 3). F N.m.r. analysis of the 3,3,3-trifluoro-l-iodopropene and 3,3,4,4,4-pentafluoro-l-iodobutene prepared by u.v.-induced addition of trifluoroiodomethane and pentafluoroiodoethane, respectively, across the multiple bond in acetylene has revealed that the irons adducts predominate (CFg-CH CHI, cwr/roras = 1 6.7 CgFs-CHiCHI, cisUrans = -Si). cis-Addition across acetylene is much more important in the case of heptafluoro-2-iodopropane, the ratio of c/j- /ra s-(CFs)2CF-CH CHI being 1 1.78. ... 

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