Perfluoro-1,3-butadiene

Fluorinated 1,3-dienes can show a strong preference for biradical [2+2] additions over concerted [4+2] additions, and perfluoro-1,3-butadiene is noton-... 

Cyclohexadiene and singlet oxygen form (103). Most of the important synthetic approaches for 1,2-thiazines use a fragment in which the S-N bond already exists. Syntheses via [4 + 2] cycloadditions constitute a major part of the synthetic repertoire for this class of compounds (CHEC-II(6)370). Thus, pentadiene with TsNSO gives (104) and perfluoro-l,2-thiazine (105) is prepared by the cycloaddition of thiazyl fluoride (FSN) and perfluoro-1,3-butadiene CF2 = CFCF = CF2 (79CC35). 

One of the simplest representatives of the thiazine class is the perfluoro derivative (126), which is prepared by the cycloaddition of thiazyl fluoride (125) and perfluoro-1,3-butadiene (Scheme 50) (79CC35). 

The yields of thermal rearrangements of some perfluorinated olefins are very low The fact that perfluorocyclobutene yields perfluoro-1,3-butadiene at 650 °C only in a 12% yield [7] is due to the higher thermodynamic stability of perfluoro cyclobutene compared with the-open chain product [724]... 

In view of results obtained in the rhodium chemistry of OFCOT (see Section VIII,F,1), the molecular formula and spectroscopic data for 65 do not allow a distinction to be made between the l,2-f/2-C8F8 and l,4-f/2-C8F8 ligation modes for the OFCOT ligand. The latter structure would also be consistent with that observed for the complex 37 formed between perfluoro- 1,3-butadiene and the [Fe(CO)4] fragment (see Section III,E). 

At 200°C, perfluoro-1,3-butadiene dimerizes. What is the structure of the dimer ... 

Cycloadditions of fluorinated dienes are known to give cyclobutane rings. The original suggestion of the structure of the dimer of perfluoro-1,3-butadiene was perfluorotricyclo[4,2,0,02 5]octane [727]. The compound did not react with potassium permanganate. Fifteen years later, another formula was found correct based on physical methods. Instead of three four-membered rings, the product consists of three five-membered rings. Its name is perfluorotricyclo[3,3,0,02 6]octane [128],... 

K from the photochemical addition of sulfur dioxide to ketene. It decomposes on prolonged irradiation at 20°K to carbon dioxide and, presumably, sulfine which could not be detected. Addition of sulfur dioxide to perfluoro-1,3-butadiene gives the (3-sultine 495. A stable (3-sultine is said to be obtained from sulfur dioxide and quadricyclane. ... 

Butadiene. 1,3-Butadiene has a well-established, planar trans (x = 180°) structure (29). A second cis-skew structure has been predicted to exist with a torsion angle (x) of 37-40° (30,31). The cw-skew structure is calculated to be 3.15 kcal/mol above the trans, and the experimental estimate of this difference is 2.5 kcal/mol (32,33). The two cis-skew structures are separated by a barrier through the cis conformer of 0.5 kcal/mol (22, 23). Perfluoro- 1,3-butadiene, however, has the cis- skew structure as the global minimum with x = 47.4 2.4° from electron diffraction measurements (34). From photoelectron and UV spectral data, x is estimated to be 42 15° (35). Our ab initio calculations gave a comparable value of 58.4° (10). Clearly, fluorine substitution substantially affects the gross structure of the butadiene. 

Table I. Torsional Potential Energy Surface for Perfluoro-1,3-butadiene...

Crystalline or solid samples (ca. 10 mg) are ground with 5 drops of nujol in an agate mortar to form a paste for subsequent CD or MCD measurement. Perfluoro-butadiene can also be used instead of nujol. Otherwise, the KBr pellet technique, for which KBr and sample should be completely dried in vacuo and ground into a fine powder, can be used conveniently. On using the KBr technique, one can often observe a different CD spectrum from that of the nujol-mull method. 

I.r. emission has been seen from the vibrationally excited CO2 product of MPD of vinylacetic and pyruvic acids, from hydrogen halides formed by chemical reaction of CI2 with H atoms produced in the MPD of various hydrocarbons, and of HBr with F and Cl atoms formed in the MPD of CFjCl. Infrared fluorescence from CjFjCl following MPA shows emission from both discrete levels and the quasicontinuum, with efficient intramolecular vibrational redistribution out of the pumped mode evident after absorption of only 2—3 photons. Emission in the i.r. has been seen following MPA in N2p4, and has been used to study the interconversion of perfluorocyclobutene to perfluoro-butadiene isomers following MPA. Further isomerization reactions induced by CO2 lasers have been reported. 

These include anionic polymerizations of some conjugated monomers such as -tri-fluoromethyl acrylates, fluorostyrene derivatives and 1,4-perfluoro-butadiene (17), and condensation polymerization to afford such aromatic fluoropolymers as polyarylates and aramides (18). In addition, fluorinated polyimides are on a way of evaluation for practical applications in the electronics field. 

Cyclopentadiene (6) reacted with 105 at 0°C to give 108 (entry 1). At 100°C, butadiene (12) afforded 109 (entry 2). No [2 + 2] cycloadduct was formed in either reaction. Perfluoromethylenecyclopropane (105) failed to react with cis,cis- or cis,trans-2,4-hexadiene at 100 °C, although 110 was readily formed from trans,frans-2,4-hexadiene (106) under these conditions [29] (entry 3). Anthracene (107) added to 105 at 100 °C. The dienophilicity of 105 is exceptional when compared with the reactivity of simple fluoroolefins, such as perfluoro-isobutylene, which require 150 and 200 °C to undergo cycloaddition to cyclopentadiene [30] and anthracene, respectively. 

Mechanistic studies of the pyrolysis of disodium peifluoropentanedioate and derivatives have shown that the acid fluorides are formed during the reaction. The formation of dienes from the salts of halogcnalcd carboxylic acids with a terminal C = C bond is also possible. The thermal decomposition of sodium (Z)-6//-perfluoro 6-chlorohex-5-cnoate) gives (Z)-l//-perfluoro(l-chloropenta-l,4-diene) (7) in 75% yield.The decarboxylation of potassium 5H-pcrfluoropcnt-4-enoate, however, gives 1//-perfluorobut-2-yne (8) via the isomerization of the intermediate butadiene by potassium fluoride. ... 

Figure 2. CPK model of perfluoro(l,3)butadiene. Image generated on a CRAY X-MP supercomputer using OASIS software. The carbons are the dark atoms and the fluorines are the light atoms.

Figure 3. Torsional potential energy surface for perfluoro(l, 3)butadiene.

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