Add time:09/08/2019         Source:sciencedirect.com

Non-conjugated dienes, with an azonitrile initiator, add one or two RFI to provide RFRH “diblock” and RFRHRF “triblock” compounds with one, or two perfluoroalkyl groups, respectively. Those diblock products with long fluorocarbon and hydrocarbon segments furnish novel surfactants for fluorocarbon liquid systems, and are cell structure modifiers for biochemical applications. In the case of 1,6-heptadiene, the perfluoroalkyl radical adds first to one end, and the adduct radical may transfer iodine from RFI to give RFCH2CHI(CH2)3CHCH2 (3). Or intervention of cyclization may intervene and the radical that is formed transfers with RFI to give cis- and trans-1-iodomethyl-2- (perfluoroalkyl)methylcyclopentanes (9a,b; Scheme. 2). AIBN initiates the free radical cyclization of 6-iodo-1-heptene, or of 3, to the cyclopentane derivatives; e.g., 9a,b from 3. Reductive cyclization of 3, and closely related iodoalkenes is induced by zinc and acid or by BuSnH4. From the ratio of linear to cyclic products in the two series (Scheme. 3) some approximate rates of cyclization are deduced. N,N′-Diallylamine adds RFI with cyclization (azonitrile) to give an iodomethylpyrrolidine (Scheme. 6) that oligomerizes by aminium salt formation. Other 1,6-heptadienoic compounds listed in the title give cyclization to five-membered ring products. exo-Cyclic and endo-cyclic alkenes elicit surprising responses to a range of reaction conditions and initiating systems. Of endo-cyclic alkenes, cyclooctene is the most, and cyclohexene is the least reactive towards addition of RFI. Cyclohexene adducts with RF groups from CF3 or (CF3)2CF to CF3(CF2)6 have structures and properties that differ significantly. The preferred conformation of the adducts varies with the RF group whether the configuration is cis- or trans. Of these adducts, only the trans-CF3I chair conformer undergoes normal equilibration. In the trans-adduct, the axial-CF3CF2 group cannot freely rotate over the ring because of axial hydrogen repulsions, and the 19FNMR spectrum gives two sets of lines with relative intensities of 3:2. trans-A and cis-B cyclohexene adducts (Scheme. 8) give 19FNMR spectra with three resonance peaks from two non-equivalent CF3 groups of the iso-perfluoropropyl group coupled to each other and to the CF group. Non-equivalence of the two CF3 groups is attributed to proximity of the CF3CFCF3 group and the large, adjacent iodine atom. Removal of iodine removes non-equivalency of the CF3 groups. Thermolysis of adducts A–D gives an equilibrium mixture of the cis/trans-isomers from which entropy and the energy content are determined. Addition of RFI to cyclohexene by SET initiation with copper gives adducts in good yield. Norbornene, or substituted norbornenes, and norbornadiene add RFI in a facile reaction initiated by azonitrile, peroxide or the SET method (Scheme. 14).

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