1,2,3,4-Tetrafluoroacridines (accompanied in certain cases by their 3-arylamino derivatives) have been prepared in one-pot fashion (via formation in situ of the corresponding Schiff bases) by heating pentafluorobenzaldehyde with a 2 molar equivalence of aniline, para-substituted anilines 4-RC 6 H 4 NH 2 (R=OMe, Me, Bu t , F, Cl, Br) or 3,5-dimethylaniline in boiling o-dichlorobenzene.

Trichloro-1,2,4-triazine reacts with cycloheptene and cyclododecene to give the 2,6-dichloropyridine derivatives 6 and 7 via an intermediate dihydropyridine formed by Diels-Alder addition and loss of N-2, and with cyclopenta-1,3-diene and indene by addition of a second molecule of alkene to the intermediate dihydropyridine. Bicyclo[2.2.1] hepta-2,5-diene and quadricyclane give mainly 2,3,6-trichloropyridine by loss of cyclopentadiene from the intermediate dihydropyridine. With hexa-1,5-diene, the dihydropyridine is trapped by an intramolecular Diels-Alder reaction, forming tricyclic compounds 17 and 18. With diallyl ether, the dihydropyridine partly undergoes intramolecular cycloaddition to give 23 and partly [1,5]-sigmatropic shift of hydrogen before intramolecular cycloaddition to give 25. With cyclododeca-1,5,9-triene formation of pyridine derivatives is incomplete and the immediate precursor can be trapped with water.

Treatment of octafluorotoluene (2) with approximately one-molar equivalents of the oximates R1R2C = NO~ M+ (R1 = R2=Me;R1 = R2 = Ph; R1 = Me, R2 = Ph;M = Na) (6a-c) in diethyl ether gives 4-(R1R2C = NO)C6F4CF3 (7a-c) as the only isolated products. Corresponding reaction of 3,5-dichlorotrifluoropyridine (3) with the oximates 6a-c affords 4-and 2-(R1R2C = NO)C5F2C12N (8a-c) and (9a-c), respectively (4-/2ratios at −35 °C: 65:35; 30:70; 12:88) ; the lithium oximates (R1 = R2 =Ph ; R1 = Me, R2 = Ph; M = Li) (6d) and (6e) give comparable results. With 3-chlorotetrafluoropyridine (4), treatment with sodium oximate 6c gives 4-(PhCMe = NO)-3-ClC5F3N (10) and 2-(PhCMe = NO)-5ClC5F3N (11) (ratio 44:56 at −35 °C). Such competition between SNAr attack of these alkali-metal oximates at the C-4 and C-2 positions of chlorofluoropyridines 3 and 4 can be rationalized by invoking chelation of an alkali-metal cation with ring nitrogen in the transition state leading to formation of an orthio-quinonoidal σ-complex. Exclusive initial attack at the C-4 ring site appears to occur in the reaction of tetrafluoropyrimidine (5) with oximates 6a and 6c to afford 4-(MeC = NO)C4F3N2 (12a) and 4-(PhCMe=NO)C4F3NN2 (12b), respectively; Some further attack on product 12b by oximate 6c at the C-6 site takes place to give the disubstituted derivative 4,6-(PhCMe=NO)2C4F2N2 (13).

Treatment of the nitroxides Et(2)NO(-) M(+) (2a-c) (M=Na, Li, K) and (Et(2)NO(-))(2) Ba2+ (2d) with pentafluoropyridine (3) at room temperature (1 d) gave in all cases the compounds Py-NEt(2) (8), Py-ONEt(2) (9), Py-NHEt (10) and Py-O(-)H(2)Net(2) (11) (where Py = tetrafluoro-4-pyridyl) in the approximate ratio 1:30:30:35. The radical traps, 1,4-dinitrobenzene or galvinoxyl, retarded the reaction (5 d required for complete consumption of 3), but the same products were formed in a similar ratio and compounds 8-11 were also formed by decomposition of the amine oxide Py-N(O)Et(2) (20) [synthesised by the route: 3 + Et(2)NH --> 8 (57%); 8 + (CF3CO)(2)O/H2O2 --> 20 (81%) as the monohydrate]. It is proposed that the products 8-11 arose mainly via an S(RN)1 mechanism involving single electron transfer (SET) from the nitroxide 2 to the substrate 3 leading to the radical anion (21) and hence the tetrafluoro-4-pyridyl radical (22) which reacted with 2 at nitrogen to afford the amine oxide 20. Major Meisenheimer rearrangement of 20 gave hydroxylamine 9, while minor rearrangement afforded the hydroxylamine Py-N(Et)OEt (23) which eliminated ethanal to yield the secondary amine 10. Competing deoxygenation of 20 gave the tertiary amine 8 and the salt 11 [synthesised by reaction of Py-OH (26) with Et(2)NH] was formed via decomposition of 8 in light (or on heating) involving homolytic fission of the weak N-O bond. Treatment of 9 with the acids AHF or CF3SO3H resulted in exothermic reaction and gave compounds 8 (27%, 11%), 10 (16%, 18%) and 11 (13%, 25%) via competing protonation at oxygen and nitrogen.The corresponding reactions of nitroxide 2a with the substrates C6HF5 (4) and C6F5CF3 (5) afforded the salt 4-H-C6F4-O- H(2)NEt(2) (12) (15%) and a mixture of the compounds 4-CF3-C6F4-R [R=ONEt(2) (13) (23%); R=NHEt (14) (2%); R=O- H(2)NEt(2) (15) (12%)], respectively, while treatment of 2a with 2-chloro-3-nitropyridine (6) and 2-chloro-5-nitropyridine (7) gave the tertiary amines 2-N,N-diethylamino-3-nitropyridine (16) (35%) or 2-N,N-diethylamino-5-nitropyridine (18) (25%) together with N-(2-chloro-3-pyridyl)-N-(3-nitro-2-pyridyl)amine (17) (13%) or N-(2-chloro-5-pyridyl)-N-(5-nitro-2-pyridyl)amine (19) (27%) via presumed S(RN)1 pathways.

Treatment of pentafluoropyridine (1) in diethyl ether with approximately 1 M equiv. of the hydrazonides Ph2C=NNHLi (3a) and Ph2C=NNLiPh (3b) under mild conditions gives good yields (62% and 83%) of 4- and 2-(Ph2C=NH)C5F4N (5a and 6a) and 4- and 2-(Ph2C=NPh)C5F4N (5b and 6b), respectively, containing unusually large amounts of 2-substituted products (5a/6a = 50:50; 5b/6b = 65:35). The increased ease of displacement of a 2-F substituent from 1 (→6a and 6b) in these cases is ascribed to chelation of the lithium cation in the transition state involved in the rate-determining step leading to formation of an ortho-quinonoidal σ-complex. Catalytic hydrogenation of a 1:1 mixture of hydrazones 5a and 6a affords the corresponding hydrazines, 4- and 2-H2NNHC5F4N (7 and 8) in good yield (78%); acidic hydrolysis (hot HCl aq.) of the 5a/6a mixture yields tetrafluoro-4-hydrazinopyridine (9) and, depending on the conditions, tetrafluoro-2-hydrazinopyridine (10) or 2-aminotetrafluoropyridine (11).

The asymmetric unit of the title compound, C18H10F4N2O, is composed of two identical molecules having different configurations. Although both molecules adopt a trans configuration about the N-O bond [C-N-O-C 164.2 (3) and -162.0 (2)-degrees], substantial twists of all the aromatic rings relative to the C=N-O plane show no correlation between the conformers. Despite the apparently random molecular configurations, the packing arrangement involves several pi interactions between adjacent molecules.

Thermal reaction (20–70 °C) of the dichloroazine CF3CCl=NN=CClCF3, 2, with cyclopentene (in CH2Cl2 solvent), cycloheptene, indene, acenaphthylene, 2,3-dihydrofuran, 3,4-dihydro-2H-pyran, norbornadiene, cyclopentadiene and dicyclopentadiene afforded, as the major product in each case, the corresponding rearranged [32] cycloadduct 3 containing a CF3CCl2N= grouping. The direction of cycloaddition to the unsymmetrical carbocycles indene and cyclopentadiene was consistent with the reactions being LUMO (azine)-HOMO (dipolarophile) controlled. On attempted Chromatographic purification on silica gel, the rearranged adducts 3 were hydrolysed to the corresponding amides 4 (=NCCl2CF3 → =NCOCF3). The cyclopentene reaction, unexpectedly, also gave the cyclopentadiene [32] cycloadduct 3b, while from the norbornadiene reaction a hydrolysed 2:1 adduct 9 (4%) was isolated by chromatography. Other products obtained by Chromatographic separation from the 3,4-dihydro-2H-pyran reaction were the substituted azine CH2(CH2)2OCH=C-C(CF3)=NN=CClCF3 (5) (29%), equimolar amounts of the ketone CH2(CH2)2OCH=C-COCF3 (6) (18%) and the chlorohydrazone O(CH2)4CH-NHN=CClCF3 (7) (18%), possibly arising via the [32] cycloadduct 15 of 5 and the pyran, and the hydrazone CH2(CH2)2OCH=C-C(CF3) =NNH2 (8) (4%), formed via 15 or by hydrolysis of the amide 4g. Treatment of amide 4d, derived from indene with ethanolic methylamine, gave the expected amino compound 21a (94%) and CF3CONHMe (22) (91%). In contrast, treatment of the exo-amide 4h, derived from norbornadiene with ethanolic methylamine, afforded the N-formyl compound 23 (87%), while corresponding treatment of a mixture of the exo- and endo-amides (4h and 4i) gave the exo- and endo-amino compounds (21b and 21c) (88%), together with compound 22 (ca. 10%) and the azapropenylindazole 24 (ca. 5%) ; compound 24 hydrolysed to 23 on storage. It is proposed that the amines 21b and 21c arose mainly via the sequence: =NCOCF3 → =N-CH=NMe (24) → =NCHO (23) → =NH.

The benzaldehyde nitrone moiety in the title molecule, N-benzylidene-4-fluoroaniline N-oxide, C13H10FNO, like that in N-(benzylidene)methylamine N-oxide [Bed-ford, Chaloner and Hitchcock (1991). Acta Cryst. C47, 2484-2485] approaches planarity [C-benz-N=C-C-benz 179.5 (5) and C-benz-C-benz-C=N -13(1)degrees cf 176.0 (2) and 6.8 (2)degrees, respectively, in the methyl compound]. However, the p-fluorobenzene substituent is substantially twisted out of the molecular plane [C-benz-C-benz-N=C -42.8 (8)degrees] in order to avoid a non-bonded O ... H. clash.

The title structure, C13H8F6N2O, is the hydrolysis product of the rearranged 1,3-dipolar cycloadduct of 2,5-dichloro-1,1,1,6,6,6-hexafluoro-3,4-diazahexa-2,4-diene and indene, and comprises approximately planar moieties meeting at a dihedral angle of 119.7(1)degrees along the shared C-C bond between the five-membered rings. One plane contains the carbonyl substituent, which lies trans to the N-N bond [O=C-N-N 179.2(3)degrees] and completes a delocalization pathway extending from the ring C=N bond [C-N-N=C -176.3 (3)degrees]. However, as the latter bond is only 1.248(4) Angstrom, long, any delocalization must be limited to the O=C-N-N region.

The dichloroazine 5 has been converted into the monoaminoazines CF3C(NHR)=NN=CClCF3 (6) [a, R = Ph (89%); b, R = H (81%); c, R = Me (89%); d, R = CH2CO2Me (96%); e, R = CH2CO2Et (95%)] and the diaminoazines CF3C(NHR) = NN = C(NHR)CF3 (4) [c, R = H (96%); d, R = Me (94%); e, R = CH2CO2Me (50%); f, R = CH2CO2Et (77%)] by reaction with ammonia or the appropriate primary amino compound; with hydroxylamine the syn-oxime CF3CCl = NNHC(CF3) = NOH (8) (86%) was formed. The mixed diaminoazines CF3C(NHR) = NN = C(NHR′)CF3 (4) [g, R = H, R′ = Ph; h, R′ = Me, R′ = H; i, R = Me, R′ = CH2CO2Me; j, R = CH2CO2Me, R′ = Ph (92%–96%)] have been synthesised from the monoaminoazines 6a-d. A solution of the diaminoazine 4c, heated in ethanol under reflux, gave 3,5-bis(trifluoromethyl)-1H,2,4-triazole (1a) (28%) and its ammonium salt NH4+[C2N3(CF3)2]− (7b) (54%), while the azines 4g and 4j under the same conditions each afforded 4-phenyl-3,5-bis(trifluoromethyl)-4H-1,2,4-triazole (2c) (ca. 85%). Thermolysis of the diaminoazines 4c-f and 4h in vacuo over the range 120–150 °C gave the following results: 4c → 7b (98%); 4d → MeNH3+ [C2N3(CF3)2]− (7c) (ca. 26%)+Me4N+ [C2N3(CF3)2]− (7d) (ca. 13%) + 4-methyl-3,5-bis(trifluoromethyl)-4H-1,2,4-triazole (2b) (54%) + 1-methyl-3,5-bis(trifluoromethyl)-1H-1,2,4-triazole (1b) (1.5%); 4e → the 4-carbomethoxymethyltriazole (2e) (93%); 4f → the 4-carboethoxymethyltriazole (2f) (82%); 4h → 1a (11%) + 2b (54%) + 7c (31%). Treatment of salt 7b with aqueous hydrochloric acid afforded the triazole 1a (75%).

Thermal reaction (70 °C) of the dichloroazine CF3CCl=NN=CClCF3, 1, with cycloheptatriene (7) gave a complex mixture from which the major products were separated and identified as the dehydrochlorinated rearranged [32] cycloadducts 9 (28%) and 10 (23%) containing a CF3CHClN= group, a rearranged 1:1 adduct (12 or 13) (4%) and the amide 14 (18%) formed by hydrolysis on silica gel of the rearranged [36] cycloadduct 31 containing a CF3CCl2N= group. At 100 °C in solvent CH2Cl2, the isolated products were the isomers 9 (4%), 10 (4%) and 11 (5.5%), amide 14 (1%) and the reduced compounds 15 (6%) and 16 (19%) containing a CF3CH2N group. Reaction between hexafluoroacetone azine (CF3)2C=NN=C(CF3)2 (5) and 7 at 70 °C was much cleaner and gave the bis[32] criss-cross cycloadduct 18 (15%), the bis-ene adduct 20 (17%) and the azo compound 19 (21%) together with the imine 17 (20%) formed from the oxidation of 20 by azine 5 and the [36] cycloadduct, the diaziridine 21 (7%).

In common with other isocoumarin-based molecules, the planar fused ring system [maximum deviation 0.05(2)A] in the title molecule, ethyl 1-oxo-6,7-bis(trifluoromethyl)-1H-2-benzopyran-3-carboxylate, C 14 H 8 F 6 O 4 , contains a non-delocalized double bond [C=C 1.34(2)A]. Pairs of molecules form π-bonded dimers, centred on inversion points at y = 1/4 and 3/4 [closest interplanar C...C approach 3.59 (3) A] Consequently, the crystal structure is composed of alternating aromatic (y = 1/4 or 3/4) and aliphatic zones (y = 0 or 1/2).

Thermal reaction of the acetylenic ester CF3CCCO2Et (1) with cyclopentadiene (4), buta-1,3-diene (5) and 1,4-diphenylbuta-1,3-diene (6) gave the corresponding Diels-Alder 1:1 cycloadducts 10, 11 and 12, respectively in high yield (73%–97%). With norbornadiene (7), the homo Diels-Alder adduct (13) was formed. The reaction with 3-carboethoxyfuran gave a mixture (55%) of the isomeric Diels-Alder 1:1 adducts 14 and 15 (ratio 55:45), together with four 2:1 adducts, i.e., the exo,endo compounds 16a (10%) and 16b (9%) and the exo,exo compounds 17a (8%) and 17b (9%), resulting from Diels-Alder cycloaddition of the furan to the least substituted double bond in the 1:1 adducts 14 and 15. The cycloadditions to the 1:1 adducts were regioselective with the two CO2Et groups on the unsaturated bonds involved in the cycloadditions being 1,4 to each other in the 2:1 adducts. The products from reaction of ester 1 with cycloheptatriene (9) were formed via two competing reaction paths; (a) cycloaddition of ester 1 to norcaradiene (23) which gave the Diels-Alder adduct 18 (74%) and (b) an initial regioselective ‘ene’ reaction followed by isomerisation of the resulting 1:1 adduct 24 to the corresponding norcaradiene 25, which then underwent both rearrangement to afford 1:1 adduct 19 (15%) and Diels-Alder cycloaddition with ester 1 to give the 2:1 adduct 20 (6%).

Thermal reaction of ethyl 4,4,4-trifluorobut-2-ynoate (1) and hexafluorobut-2-yne (2) with quadricyclane (3) gave the exo-1:1 adducts (4a) and (4b), respectively, by a (σ2s+σ2s+η2s) cycloaddition pathway. Hydrogenation (1 mol equiv. of hydrogen) of adducts 4a and 4b using a PdC catalyst resulted in addition to the least substituted double bond to afford the alkenes 5a and 5b, respectively, and further hydrogenation of alkene 5a gave the alkane 6. Flow pyrolysis of adduct 4a at 450 °C yielded cis,cis,cis-3-carboethoxy-4-trifluoromethylbicyclo[4.2.1]nona-2,4,7-triene (7a) (30%) and a ca. 1:1 mixture (55%) of cis,cis,cis-4-carboethoxy-3-trifluoromethylbicyclo[4.3.0]nona-2,4,7-triene (8a) and its 3-carboethoxy-4-trifluoromethyl isomer (8b). Compound 7a arose by a non-concerted ring-opening of adduct 4a, and compounds 8a and 8b were formed via an intramolecular Diels-Alder reaction of 7a followed by rearrangement involving a 1,2-hydrogen shift. On flow pyrolysis under identical conditions, adduct 4b afforded the rearranged triene 8c exclusively, while flow pyrolysis of alkenes 5a and 5b gave the corresponding cis,cis-bicyclo[4.2.1]nona-2,4-dienes 9a and 9b, respectively. Attempted 1,3-dipolar cycloaddition between diene 9a and dia-zomethane, and Diels-Alder reactions between diene 9b and alkyne 1 or ethyl propynoate, were unsuccessful.

Despite the oxyimino chain being unconjugated [N-O 1.434 (2) and C-N 1.278 (2) angstrom] in the title compound, C13H8F4N2O, the planar alpha-phenylethylimino and tetrafluoro-2-oxopyridine moieties are only slightly twisted relative to each other [C-O-N-C 167.6 (2)-degrees]. This facilitates stacking along the ac diagonal so that fluorinated pyridine substituents alternate with non-fluorinated phenyl rings.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

In the title molecule, C21H17FN2O3, the five-membered ring adopts an envelope conformation, folded between sites 2 and 5, with a flap angle of 42.0 degrees. This configuration places the three substituents in axial positions with the fluorophenyl group attached to the N atoms trans to the other two aromatic rings.

In 2-(2,6-difluorophenyl)-1,3-diehiane, (1), C10H10F2S2, described here, and its unfluorinated counterpart [Kalff and Romers (1966). Acta Cryst. 20, 490-496], the conformation about the C-C bond joining the two rings is similar, with S-C-C-ar-C-ar torsion angles of 59.5(2) and -67.6(2)degrees in the former, and 59.7 and -66.0 degrees in the latter, In the oxidation product 2-(2,6-difluorophenyl)-1,3-dithiane 1,1,3,3-tetraoxide, (2), C10H10F2O(4)S(2), the torsion angles become 42.8(4) and -87.6(3)degrees. There is a slight flattening of the tetrahedral geometry at atom C2, as indicated by the sum of the three non-H bond angles [335.7(2) and 340.8(3)degrees for (1) and (2), respectively], Compound (2) is not unduly sterically congested since the shortest O ... F contact 2.712 (3) Angstrom is close to the expected van der Waals distance of 2.75 Angstrom. However, further twisting about the central bond would lead to an unacceptably short O ... F contact of 1.501 Angstrom, effectively blocking free rotation of the phenyl ring about this bond.

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The reaction of triethylamine with the title azine 1 (2:1 molar ratio) in light gives, as the major product, an orange liquid considered previously to be the Δ2-azetine CF3CCI=N-N-C(CF3)=CHCHNEt2 (3), but now shown to be the open-chain isomer, i.e. the triazadecatriene CF3CCl=NN = C(CF3)CH=CHNEt2 (4) by a comparison of its 1H, 13C and 19F NMR spectra with those of its solid amino derivative CF3C(NH2)=NN=C(CF3)CH=CHNEt2 (6) (made in 96% yield by reaction of compound 4 with ammonia) the structure of which has been established by X-ray crystallography. A second reaction using a large excess of triethylamine (6:1 molar ratio in light followed by heating at 115 °C) affords compound 4 (17%), its diethylamino derivative CF3C(Net2)=NN=C(CF3)CH=CHNEt2 (8) (12%), the tetra-azatetradecatetraene Et2NCH=CHC(CF3)=NN=C(CF3)CH=CHNEt2 (9) (6%) and the hydrolysis product of compound 9, the dienol N=C(CF3)CH2CHNC(CF3)=CHCH(OH)O (10) (2%). Treatment of compound 9 with silica gel gives the dienol 10 (84%). The reaction of the triazadecatriene 4 with 1-diethylaminocyclopentene (5) (1:2 molar ratio) affords the 2-substituted enamine CH2(CH2)2C(Net2)=C-C(CF3)=NN=C(CF3)CH=CHNEt2 (17) (74%) and this on hydrolysis (silica gel) gives the corresponding 2-substituted ketone O=C(CH2)3CHC(CF3)=NN=C(CF3)CH=CHNEt2 (18) (75%) and the pyrazole derivative O=C(CH2)3C=C(CF3)NN=C(CF3)CH= CH (19) (15%).