A variable temperature study of the 19-F N.M.R. spectrum of perfluorohexamethyltetrazan: Novel restricted rotation and hindered inversion at the nitrogen atoms [1]

At low temperatures, the ¹⁹F n.m.r. spectrum of the tetrazan (CF₃)₂NN(CF₃)N(CF₃)N(CF₃)₂ shows the presence of two isomers with a free energy difference in stability Δ$\text{G}$ of 2.2 kJ mol^-1. Both isomers show three types of CF₃ group which coalesce at -15°C to three systems of equal intensity (Δ$\text{G}$≠ 52 kJ mol^-1). At 40 °C the two signals assigned to the terminal CF₃ groups coalesce to a single band (Δ$\text{G}$≠ 65 kJ mol^-1).The behaviour is discussed in terms of restricted inversion at the nitrogen atoms, and hindered rotation about the N-N bonds.The hydrazines (CF₃)₂NN(CF₃)NO and (CF₃)₂NN(CF₃)NO₂ have temperature independent spectra.     

Nuclear magnetic resonance spectra of polyfluorobuta-1,3-dienes. Part II [1]. Variable temperature study of two 2-azabutadienes

The two perfluoro-azadienes CF₂N.CRCF₂ (R = CF₃ or CF₂Cl) show temperature dependent ¹⁹F n.m.r. spectra, with non-equivalent fluorine nuclei of the CF₂N portion at low temperatures, which coalesce due to inversion at the nitrogen at higher temperatures (ΔG3 = 60 kJ mol^?1). N.m.r. parameters have been obtained. One of the five-bond FF coupling constants is much larger ($\text{ca}$. 24 Hz) than the remainder (0·5–5·5 Hz), possibly due to ‘through-space’ coupling of fluorines in the $\text{cis}$-skew conformation.     

Fluorocarbon derivatives of nitrogen. Part IV [1]. Perfluoro-1-azacyclohex-1-ylcaesium

Caesium fluoride combined with perfluoro-1-azacyclohexene in acetonitrile to yield perfluoro-1-azacyclohex-1-ylcaesium (1), which was characterised by ¹⁹F n.m.r. spectroscopy and by treatment with iodomethane to give 2,2,3,3,4,4,5,5,6,6-decafluoro-1-methyl-1-azacyclohexane (2). Attempts to derivatize the caesium salt with chlorotrimethylsilane provided fluorotrimethylsilane, perfluoro-[1-(1-azacyclohex-1-en-2-yl)-1-azacyclohexane] (4), and 2-chloro-3,3,4,4,5,5,6,6-octafluoro-1-azacyclohexene (5); information on the course of this reaction was obtained through experiments in which perfluoro-1-azacyclohexene was shown to undergo conversion into its chloro-analogue (5) and its dimer (4) $\text{via}$ treatment with chlorotrimethylsilane and fluoride ion, respectively. Aluminium chloride also converts perfluoro-1-azacyclohexene into its chloro-analogue (5).     

N-halogeno-compounds. Part II [1]. N.M.R. data for polyfluorocyclohexadienylideneamines obtained via N- chlorination of polyfluoroarylamines

N.m.r. parameters for nine (I-IX) $\text{N}$-chloropolyfluorocyclohexa-2,5-dienylideneamines are reported and discussed; the magnitudes of the FF-coupling constants fall into the following ranges:

$\text{J}$₁₂ 0-2.8; $\text{J}$₁₃, $\text{J}$₃₅ 6.0-6.8; $\text{J}$₁₄ <1; $\text{J}$₁₅ 0-2.6; $\text{J}$₂₃, $\text{J}$₃₄ 25.5-27.2; $\text{J}$₂₄ 0-6.0; $\text{J}$₂₅ 0-1.2; $\text{J}$₄₅ 5.4-9.8 Hz (I) X = Y = Z = F; (II) X = OMe, Y = Z = F; (III) X - CF₃, Y = Z = F; (IV) X = Ph, Y = Z = F; (V) X = Cl, Y = Z = F; (VI) X = Br, Y = Z = F; (VII) X = Y = F, Z = Cl; (VIII) X = Y = F, Z = Br; (IX) X = Z = F, Y = H. The spectra of $\text{N}$-methyl-4-chloropentafluorocyclohexa-2,5-dienyldeneamine have also been analysed. All the imines examined are configurationally stable at the nitrogen atom.     

Fluorocarbon derivatives of nitrogen. Part 11. Synthesis of some 2-(trifluoromethyl)imidazo[1,2-a]pyridines from trifluoroacetonitrile

3-(t-Butoxycarbonyl)-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine, prepared from trifluoroacetonitrile and pyridinium t-butoxycarbonylmethylide, reacts smoothly with trifluoroacetic acid to provide 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine-3-carboxylic acid, which gives 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine when heated. 3-Cyano-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine can be obtained $\text{via}$ treatment of trifluoroacetonitrile with pyridinium cyanomethylide, which is sufficiently reactive to effect nucleophilic displacement of fluorine from pentafluoropyridine under mild conditions [→pyridinium cyano(tetrafluoro-4-pyridyl)methylide].     

Fluorocarbon derivatives of nitrogen. Part VII [1]. Reaction of N-iminopyridinium ylide with perfluoro-1-azacyclohexene,perfluoro-2-azapropene,and perfluoroacetonitrile

The novel ylides (II) and (III) have been obtained $\text{via}$ treatment of perfluoro-1-azacyclohexene and perfluoro-2-azapropene, respectively, with $\text{N}$-iminopyridinium ylide (I) generated $\text{in}$$\text{situ}$ from $\text{N}$-aminopyridinium iodide and anhydrous potassium carbonate in methylene chloride. A mixture of the $\text{s}$-triazolo[1,5-$\text{a}$]pyridine (IV) and a compound thought to be its dihydro-analogue (V) were isolated following attack on perfluoroacetonitrile by the parent ylide (I); the former product was also prepared by heating 1,2-diamino-pyridinium iodide with trifluoroacetic anhydride.     

Fluorocarbon derivatives of nitrogen. Part I. Some reactions of perfluoro-1-azacyclohexene

Controlled displacement of fluorine from perfluoro-1-azacyclo-hexene (I) by the nucleophilic reagents Me₂NH, Et₂NH, $\text{CH}{}_2\text{CH}{}_2\text{O(CH}{}_2\text{)}{}_2\text{N}$H, C₆Cl₅ONa, and (CF₃)₂NONa provides the derivatives (II) - (IV), respectively. The last of these can also be obtained by treatment of the parent compound (I) with mercury^II bistrifluoromethylnitroxide.     

Studies in azide chemistry. Part 12. One-pot conversion of 4-azidotetrafluoropyridine to 1,3,4-trifluoro-7,9-dimethyl-11H-pyrido[4,3-c]benzo[1,2]diazepine

Thermolysis of 4-azidotetrafluoropyridine in the presence of an excess of mesidine at 170 °C yields tetrafluoro-4-(2,4,6-trimethylphenylazo)- pyridine, which undergoes intramolecular dehydrofluorination $\text{in situ}$ to provide 1,3,4-trifluoro-7,9-dimethyl-11$\text{H}$-pyrido[4,3-$\text{c}$]benzo[1,2]diazepine.     

Fluorocarbon derivatives of nitrogen. Part 10. Preparation of heptafluoro- and 1-chlorohexafluoro-2-nitrosopropane,and conversion on the latter to chloropentafluoroacetone oxime

Details are given for the preparation of heptafluoro-2-nitrosopropane and 1-chlorohexafluoro-2-nitrosopropane $\text{via}$ the routes CF₃CFCF₂ → [with CsFR_FCO₂Ag (R_F = CF₃, nC₃F₇)] (CF₃)₂CFAg → (with NOCl) (CF₃)₂CFNO and CF₃CFCF₂ → (with CsClNOCl) CF₃(CF₂Cl)CFNO, respectively, and for conversion of the latter nitroso-compound to chloropentafluoroacetone oxime $\text{via}$ reduction with aqueous potassium hydrogen sulphite.     

Some reactions of 1,2,3,4,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene: Thermolysis and attack by methoxide ion and by bistrifluoromethyl nitroxide

1,2,3,4,7,7-Hexafluorobicyclo[2,2,1]hepta-2,5-diene gave 1,2,3,4-tetrafluorebenzene in at least 73% yield when heated to 450°C in a sealed tube; the CF₂ bridge appeared, in part, as octafluorocyclobutane. Nucleophilic attack by sodium methoxide- methanol on the diene occurred exclusively at the CFCF bond, causing the formation of 1,2,4,7,7-pentafluoro-3-methoxybicyclo- [2,2,1]hepta-2,5-diene and a 1,4,5,6,7,7-hexafluoro-5-methoxybicyclo [2,2,1]hept-2-ene thought, on the basis of ¹⁹F nmr data, to be the 6-$\text{endo}$-F,5-$\text{exo}$-MeO isomer. Radical attack on 1,2,3,- 4,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene by bistrifluoromethyl nitroxide took place at both olefinic sites, with a $\text{ca}$. 10:1 preference for the CFCF linkage; all three geometrical isomers of 5,6-bis(bistrifluoromethylamino-oxy)-1,4,5,6,7,7- hexafluorobicyclo[2,2,1]hept-2-ene were formed.     

A novel synthesis of 3-fluorophenylalanine and some of its derivatives

Ring opening of 2-cyano-3-phenylaziridine and 2-amido-3-phénylaziridine by HF/pyridine was found to give 2-amino-3-fluorophenylpropionitrile (IV) and 2-amino-3-fluorophenylalanamide (VII) respectively. 3-fluorophenylalanine (V) could be obtained by an acidic hydrolysis of (IV) or (VII) whereas isopropyl-3 fluorophenylalanate (VI) was isolated by esterification of (V) or by heating (IV) with iso-propanal-12 NHCl under reflux.     

Fluoro-olefin chemistry Part 20 [1]. Reaction of hexafluoropropene with alcohols

Reaction of hexafluoropropene (HFP) with a series of alcohols under thermal, photochemical or peroxide-initiated conditions affords the 1:1 adducts CF₃CHFCF₂CR¹R²OH (R¹ = H, R² = H, Me, Prⁿ or CF₃; R¹ = Me, R² = Me or Et) in high yield via a radical chain mechanism. Adduct are not formed with the alcohols (CF₃)₂CHOH and CF₃CHFCF₂CH₂OH. Other 1:1 adducts of structure CHF₂CF(CF₃)CH₂OH and CH₃(C₂H₃CF₂CHFCF₃)CH₂OH are formed as minor products in the methanol and $\text{n}$-butanol reactions, respectively.     

A comparative study of polyurethane-poly(methyl methacrylate) interpenetrating and semi-1 interpenetrating polymer networks

Polyurethane(PUR)-poly(methyl methacrylate) (PAc) semi-1 interpenetrating polymer networks of various compositions have been prepared. They show several differences from the corresponding full IPN's. Thus, the rate of polymerization of the acrylic phase is lower. Transparent plates are also more difficult to obtain. Both effects are ascribed to the absence of the crosslinking agent of the second phase. The composition also plays a role in transparency. Solvent extraction shows that, with increasing PUR content, more PAc remains entrapped in the PUR network. The transition behaviour indicates that the phases are less entangled in semi-IPN's than in IPN's. Consequently, the effect of crosslinking or not crosslinking the second component is very important with regard to the properties of PUR/PAc combinations.     

Studies in azide chemistry. Part IX [1]. Investigations involving fluorinated azidopyrimidines and 4-azido-3-chloro-2,5,6-trifluoropyridine

4-Azido-2,5,6-trifluoro- and 4,6-diazido-2,5-difluoro- pyrimidine were obtained by treating tetrafluoropyrimidine with sodium azide in acetonitrile; similar azidation of 5-chlorotrifluoropyrimidine gave 4-azido-5-chloro-2,6-difluoro- and 4,6-diazido-5-chloro-2-fluoro-pyrimidine. Each monoazide reacted with triphenylphosphine to yield the corresponding iminophosphorane (Staudinger reaction), and the trifluoro- compound gave cycloadducts when heated with phenylacetylene [→ 4-phenyl-1-(2,5,6-trifluoro-4-pyrimidinyl)-1,2,3- triazole] and acrylonitrile [→ 2-cyano-1-(2,5,6-trifluoro- 4-pyrimidinyl)aziridine]; attack on the trifluoro-azide by the sodium salt of pentafluoroaniline produced 4-azido-2,5- difluoro-6-(pentafluorophenylamino)pyrimidine and bis(4- azido-2,5-difluoro-6-pyrimidinyl)(pentafluorophenyl)amine. Attempts to intercept nitrenes during thermal decomposition of both mono-azides failed. Thermolysis of 4-azido-3-chloro- 2,5,6-trifluoropyridine in the presence of dimethyl sulphoxide, cyclohexane, or pentafluoroaniline gave products [py_FNS(O)Me₂, py_FNHC₆H₁₁, and py_FNNPh_F (PY_F = 3-chlorotrifluoro-4-pyridyl), respectively] compatible with release of the corresponding nitrene.     

Absolute configuration of ageratriol : A germacranic sesquiterpene from Achillea ageratum L.

On the basis of chemical evidence, the stereostructure 7 is proposed for ageratriol, a germacranic sesquiterpene isolated from Achillea ageratum L.