Friedel-Crafts reactions of 2,2-difluorocyclopropanecarbonyl chloride: unexpected ring-opening chemistry

The Friedel-Crafts reactions of 2,2-difluorocyclopropanecarbonyl chloride with various arenes did not lead to the straightforward formation of the expected aryl 2,2-difluorocyclopropyl ketones. Instead the reactions proceeded, to various degrees depending on the reactivity of the arene, via an apparent rearrangement of the initially formed acylium ion to form novel aryl 3-chloro-3,3-difluoropropyl ketones. The ring-opened product was formed exclusively, and therefore the reaction may be synthetically useful when relatively unreactive arene substrates such as benzene, toluene, and p-xylene are used. No conditions were found where ring-intact products could be formed exclusively when using substituted benzenes as substrates, with the very reactive substrate thiophene being most selective in that regard, favoring ring intact product 3 with a selectivity of 98:2. The regioselectivity of ring-opening was examined and compared with other related systems computationally.     

Sequential ene, Diels-Alder reactions of AF4-yne with 1,3,5-cycloheptatriene

(4,5-Dehydro)-1,1,2,2,9,9,10,10-octafluoro [2.2]paracyclophane (AF4-yne) undergoes an ene reaction with 1,3,5-cycloheptatriene, the adduct of which subsequently undergoes a further Diels-Alder reaction with a second equivalent of AF4-yne to give two stereoisomeric 2:1 adducts. A very small amount of the classic 1:1 Diels-Alder adduct also can be isolated from the reaction. Structure assignments of all products were determined by NMR through a series of H1-H1, H1-C13 one bond, and H1-C13 two and three bond correlation experiments as well as H1-H1 NOE experiments.     

Multiple electrophilic substitution of 1,1,2,2,9,9,10,10-octafluoro

Synthetic methods for introduction of two substituents into the rings of octafluoroparacyclophane are presented. Nitration gives three isomers with nitro substituents on different rings: pseudo-ortho, pseudo-meta, and pseudo-para, in equal amounts. These dinitro compounds are shown to be precursors of a variety of other disubstituted OFP derivatives. Methods of characterization of isomeric disubstituted OFPs are extensively discussed, and the 1H and 19F NMR spectra of these derivatives are analyzed explicitly.     

A highly pyramidalized cage alkene formed via the double Diels-Alder cycloaddition of syn-4,5,13,14-bis(dehydro)octafluoroparacyclophane to anthracene

[reaction: see text] A double Diels-Alder reaction of the formal syn-bis(dehydro)octafluoroparacyclophane with anthracene leads to formation of a novel cage compound that contains a highly pyramidal double bond. The measures of pyramidality of this double bond constitute what appear to be the highest combined values of psi and phi (34.3 degrees and 33.5 degrees, respectively) yet reported to have been determined by X-ray crystallography. This cage compound, although stable indefinitely as a crystalline compound in air, exhibits the high reactivity with both triplet and singlet O2 in solution that is characteristic of such highly pyramidal pi systems.     

A convenient and efficient method for incorporation of pentafluorosulfanyl (SF5) substituents into aliphatic compounds

Both SF₅Cl and SF₅Br undergo smooth, high yield addition to alkenes and alkynes under the mild free radical chain reaction conditions of triethylborane initiation at low temperature, although the SF₅Br chemistry is somewhat limited by its competing high electrophilic reactivity with electron rich alkenes. The SF₅Cl addition reaction is relatively insensitive to a wide variety of non-allylic functionalities.     

Fluorinated allenes: the syntheses of 1-fluoropropadiene, 1,1-difluoropropadiene and 1,1-difluoro-3-methyl-1,2-butadiene

Improved syntheses of 1-fluoropropadiene and 1,1-difluoropropadiene are presented as is the synthesis of a third reactive allene, 1,1-difluoro-3- methyl-1,2-butadiene. Gram quantities of these highly reactive fluorinated allenes may be prepared conveniently in high yield and purity. All three are reactive dienophiles and cycloadd regiospecifically using their non- fluorine-substituted double bonds.     

New industrial fluoropolymer science and technology

Teflon® AF, a family of copolymers of perfluoro-2,2-dimethyldioxole with tetrafluoroethylene, and Cytop®, a ring-cyclized homopolymer of CF₂=CFO(CF₂)₂CF=CF₂ are the first commercial amorphous perfluoroplastics which combine high optical clarity and solubility with outstanding chemical, thermal and electrical properties. The processes for making these materials are described and recent structure-property studies that reveal dramatic substituent effects on polymer T_g and related properties are reviewed. The results of some initial fundamental kinetic studies on fluorinated free-radical cyclizations that relate to efficient cyclopolymerization of fluorinated dienes and the design of new ring-containing fluoroplastics are discussed.     

A Novel, Non-High-Dilution Method for Preparation of 1,1,2,2,9,9,10,10-Octafluoro

A novel synthesis of octafluoro[2.2]paracyclophane (AF4), one that remarkably does not require the use of high dilution methodology, is presented. Using this unprecedented methodology, AF4 is produced in 60% yield in a reaction of Zn with 0.35 M p-bis(chlorodifluoromethyl)benzene in DMA at 100 degrees C. The process comprises a convenient, inexpensive, and highly scaleable preparation of AF4 for both research and commercial purposes.     

New synthesis of 3-fluoropyridine derivatives

The reaction of 2,2-bis(dimethylamino)-3,3-difluoro-1-methylcyclobutane-carbonitrile with alkyl lithiums leads to the formation of 6-alkyl-2-(dimethylamino)-3-fluoro-5-methylpyridines in moderate to good yields.     

Density functional theory calculations of the effect of fluorine substitution on the cyclobutylcarbinyl to 4-pentenyl radical rearrangement

The effects of fluorine substitution on the cyclobutylcarbinyl to 4-pentenyl radical rearrangement and on the strain of cyclobutane have being studied using density functional theory, the ring-opening being modestly inhibited and the strain generally not greatly affected. Perfluorocyclobutane is predicted to have 6 kcal/mol less strain than cyclobutane. Cyclizations of 1,1,2,2-tetrafluoro- and 1,1,2,2,3,3-hexafluoro-4-pentenyl radicals should be significantly enhanced ( approximately 2400 times faster) relative to the parent system. The calculations are consistent with the few experimental data available.