Al-Ahmadi, Abdullah A

Awad, Mohamed K

Moustafa, Ahmed H

NOPR

Indian Journal of ChemistryVol. 37B, May 1998, pp. 433 - 438Enhanced reactivity of pyridin-3-o1 towards 4-phenyl-l, 2, 4-triazoline-3, 5-dione: FMO treatment of the cycloaddition processAhmed H Moustafa", Abdullah A AI-Ahmadi & Mohamed K AwadFaculty of Applied Sciences, Umm AI-Qura University, Makkah, Saudi ArabiaReceived 16 November 1996, revised and accepted 26 February 1998Pyridin-3-ol reacts extremely fast as 41t electrocyclic component across the 2- and 6-positions of thepyridine ring with the potent azo-dipolarophile, 1, 2, 4-triazoline-3, 5-dione. Structural and configura-tional assignments are deduced from elemental and spectral evidence. FMO treatment of the enhanced 1,3-dipolar character of pyridin-3-ol towards the cis-azo-dipolarophile has been performed using ASED-MO calculations method.A convincing body of evidence, based largely onspectroscopic data"? have confirmed that pyridin-3-01 la in solutions in polar solvents exists to aconsiderable extent with the unstable mesomericbetaine, pyridinium-3-oxide lb. Now, pyridinium-3-oxides fall within the class of azomethine ylidesand are considered as an octet-stabilized I, 3-dipole without an orthogonal double bond. MOcalculations" and experimental data? have con-finned that such type of compounds behave aspericyclic components having [4n] x-I, 3-dipoleacross the 2- and 6-positions and/or [4n+2] x-I, 3-dipolarophiles across 2- and 4-positions. The reac-tion of pyridin-3-ol la with acrylic acid addends,acrylonitrile and methyl acrylate constitute simpleone-pot high yield conversions into-tropane-likecompounds", However, it failed to react as 4n-I,3-dipole towards many other electron-deficient ad-dends like N-phenylmaleimide, 2- and 4-vinylpyridine, diethyl maleate and, fumarate, di-ethyl azodicarboxylate, phenyl vinyl and divinylketone, chalcones, methyl cinnamate, styrene,crotononitrile, methacrylonitrile, methacryalde-hyde, phenyl propiolate, tetracyanoethylene andfumaronitrile" Now, we wish to describe herein theencouragement of the latent I, 3-dipolar characterof pyridin-Lol towards the potent 1, 3-dipolarophilc, +phenyl-I, 2, +triazoline-J, 5-dione.As anticipated, the 4-phen)'I-I, 2, 4-triazoline-3,5-dione having the cis-am-linkage proved to be apotent dipolarophile, reacting rapidly as 2n-component at low temperature with pyridin-Jsol as4n-electrocyclic component. When the reactionwas carried out in I: 1 molar ratio at -10°, the onlyproduct isolated was identified as I(H )-5-phenyl-1, J, 5, 7-tetrazatricyclo[5.3.1.03,7] undeca-9-en-4,.6, II-trione 2 from the elemental analysis andspectral evidence. When the reaction was repeatedwith two moles of the dipolarophile the only iso-lated cycloadduct was identified from the elemen-tal analysis and spectral evidence as 1-(4-phenyl-3,5-dioxo-I, 2, 4-triazolidin-I-yl)-5-phenyl-I, 3,5, 7-tetrazatricyclojc.Ll.tr'"] deca-9-en-4, 6, II-trione3. The elimination of molecular nitrogen in theionization chamber led us to investigate the ther-mal stability of the isolated adducts 2 and 3. Thus,sublimation of 2 and 3 under reduced pressure inair of nitrogen afforded, 1(H)-4-phenyl-I, 4-diazabicyclo[3.3.I]nona-7-en-3, 5, 9-trione 4 and1-(4-phenyl-3, 5-diono-I, 2, 4-triazolidin-I-yl)-5-phenyl-I, 4-diazabicyclo[3.3.I]nona-7-en-3, 5, 9-trione 5 (Scheme I) respectively.The structures for 4 and 5 were confirmed fromelemental analyses and spectral evidence (IR,IH NMR and mass). Elemental analyses indicatedthe loss of molecular nitrogen during the sublima-tion. This was tentatively established from themass spectra of 4 and 5 which displayed the ex-pected molecular ions, [M-N2J. The mass spectrumdisplayed the expected molecular ion at m1z 417a.m.u. (cf. Scheme I).434 INDIAN ] CHEM, SEC.B, MAY 1998o~1\ .~~'~o1:1(4)In earlier publication, Katritzky had reported thehigh dipolar reactivity of pyridin-Lol with onlymonosubstituted acrylic acid addends", He haspostulated two possible pathways for the formationof the isolated cycloadducts from these reactions:(i) Initial reaction of the monomer betaine lb withthe monoene to yield the cycloadducts with an NHgroup which subsequently reacted with a furthermolecule of the addend by a Michael-type addi-tion; (ii) Alternatively, the N-substittited pyridin-ium-3-oxide (type 7) resulting from the direct re-action between the addend and the nitrogen atomof the pyridin-J-ol la, with the initially formed.Zwitter ions (type 6) undergoing tautomerisation tothe N-substituted pyridinium-3-oxide 7, which re-acts with the addend to give the cycloadducts". Re-cently, we have reported the lower dipolar reactiv-ity of pyridin-Lol and its I-methyl- and 1-phenylpyridinium-Jsoxides with the trans-disubstituted olefins, l3-nitrostyrenes1o andbenzalacetophenone". The isolation of the corre-sponding ether 8 as the major product togetherwith the 2, 6-cycloadducts 9 (Scheme II) as theScheme Iminor product, indicated that the ether 8 could beobtained via inter or intramolecular rearrangementof the initially formed N-substituted pyridinium-3-oxides (type 7) prior to the cycloaddition process(pyridine reacts with maleic acid", acetylenedicar-boxylate':' and p-benzoquinone14 to produce Zwit-ter ions). Presumably, the high dipolar reactivity ofpyridin-Jsol with acrylic acid addends supports theformation of the reactive Zwitter ions (type 7) inthe first step in order to encourage the latent I, 3-dipolar character of the pyridin-Jvol.The isolation of the I: I adduct 2 and the 1:2 ad-duct 3 with 4-phenyl-l, 2, 4-triazoline-3, 5-dioneindicated that the cycloaddition process has takenplace with the Zwitter ion Ib prior to the Michaeladdition process. Presumably; the energy barrier ofthe cycloaddition process is smaller than that forthe Michael addition. The enhanced reactivity ofpyridin-J-ol as 41t-electrocyclic component with 1,2, 4-triazoline-3, 5-dione as 21t component led usto calculate the energy gap between the interfron-tier molecular orbital (HOMO and LUMO) energylevels in both reactants using ASED-MO calcula-MOUSTAFA et 01. : REACTIVITY OF PYRIDIN-3-OL TOWARDS cis-AZO-DIPOLAROPHILE 435OOH eyo~I==-~~ ~+ +IH(II) (l h)[4 + 2]H XUr=;Y HY = C6HS • X = C6Hs_ COY = C6HS' X = N02MichaelHr/)fyOYH XLJr=;Y HMichaelH XLJr=;Y H[4+2](9)Scheme IItions method of (cf Appendix). The optimizationof the 1, 2, 4-triazoline-3, 5-dione has been per-formed by optimizing its bond lengths, bond anglesand dihedral angles. The calculations produce astable structure with a minimum energy when thetriazoline ring rotates around C)-N, bond by 53<>(Figure 1). The charge density distributions overthe whole skeleton of the triazoline system and thebond orders obtained from the calculations areshown in Figure 2. The electronic structure of thetriazoline. system is also investigated using thesame method. Considering the frontier molecularorbital energies (HOMO and LUMO), the calcula-tions produce a very small energy separationwithin the triazoline system, 0.567 eV, which indi-lr"Y0H~J~X(6)~O~0~xH(7)J XN°0~~J Y(8)Figure 1Figure 1436 INDIAN J CHEM, SEC.B, MAY 1998_ 11 ~. -9LUMO ••~-12~N1P-10~'-lOMO 11:>, -e'13 . ~ -IIQJ- cr ~cW uc:w-14 -12 -H---(b) (a) (c)-15 -13Figure 3---The calculated electronic structure oftriazolinecates a high reactivity of the molecule (Figure 3).This is in accord with the experimental observa-tions. The calculations show that the lowest energytransition corresponds to n-Hc* transition whichmainly described by one electron excitation fromthe HOMO level, -12.208 eV, with considerablecontribution from nitrogen's lone-pairs, to the lowlying LUMO level, -I 1.641 eV, with complete 1t*character. The frontier orbital of the reactive spe-cies of pyridin-S>ol, pyridinium-3-oxide Ib wasalso investigated using the same method in order todecide if the cycloaddition process between pyri-dinium-3-oxide and the triazoline is HOMO beta-ine-controlled (Sustmann Type I) or LUMO beta-ine-controlled (Sustmann Type III) (Figure 4). Thecalculations produce a very small energy separa-tion between the dipole HOMO level and theLUMO level of the dipolarophile, tnazoline systemwith 0.246 eV compared with that between theLUMO betaine and the HOMO triazoline system,3.145 eV. This is clear indication that thecycloaddition of pyridin-S-ol with 1, 2, 4-triazoline-3 5-dione is HOMO betaine-controlled process,(Sustmann type 1). The HOMO-LUMO energyseparations between pyridinium-3-oxide andacrylonitrile was also calculated using the samemethod in order to correlate the reactivity of pyridin-3-01 towards acrylonitrile with that of triazolinedione. It was shown that the energy differencebetween the dipole HOMO and the LUMO of theacrylonitrile, is 2.442 eV, which is smaller than thatof the reverse one, 3.678 eV.Stereo selectivity-N-Phenylmaleimide was re-acrylonitrile pyridinium- J-o~ide lrililolineFigure 4--The calculated energies of the frontier molecularorbitals (HOMO and LUMO)ported to react with s-trazinyl betaines 15 to yieldexclusively the exo-adducts. This is contrary toPMO-FMO theory for [41ts+21tsl processes whichshould proceed preferentially via the endo-transition state. Dinitrophenyl'" and nitropyridyl"betaines yielded exclusively the endo-adducts. Itwas assumed that the formation of the exo-adductis attributed to the long reaction time under refluxwhere the initially formed endo-adduct is isomer-ised to the more thermodynamically stable exo-adduct (cf. addition of furan to maleic anhy-dride"). !n our case, it is not possible to assign theconfiguration of both Sp3-hybridized nitrogenatoms N} and N7 in the isolated cycloadducts 2 and3. H-2 and H-8 are the key protons used for as-signment of the stereochemistry of the fused tri-azolidine ring, each displayed a doublet. It is sus-pected to assign the endo-configuration for the tri-azolidine ring in 2 and 3, because the reactionshave been completed at low temperature in fewminutes, the reactions may be considered as a fast-stereo specific. This is· supported from the calcula-tion of the energy of the frontier orbitals of the re-aJrt~nts. The calculations show a stabilization of~e~U¥O level in the dipolarophile which fa-vours the endo-transition state via a secondary or-bital overlap,Experimental SectionMelting points were determined on a Gallenk-amp melting point apparatus and are uncorrected.IR spectra were recorded on a Pye-Unicam modelMOUST AFA et al. : REACTIVITY OF PYRIDIN-3-0L TOWARDS cis-AZO-DIPOLAROPHrLE 437SP 300 fR spectrophotometer and 'H NMR spectrain CDCI3 on a Varian EM-390 spectrometer usingTMS as an internal reference (chemical shifts in 8,ppm). All compounds were purified over a columnof neutral alum in? (Fluka). Elemental analyseswere performed in microanalytical laboratory atthe University of Ain Shams, Cairo. Mass spectrawere carried out on' FAB MS UMIST MS 50 TCManchester, U K.1(H)-5-Phenyl-l, 3, 5, 7-tetrazatricyclo[5.3.1.03,7] undeca-9-en-4,6,1l-trione 2. 4-Phenyl-1, 2, 4-triazoline-3, 5-dione was prepared accord-ing to Cookson et al.'9 from the oxidation of 4-phenyl-I, 2, 4-triazolidine-3, 5-dione using t-butylhypochlorite in dioxan at room temperature, theazo-compound was obtained in high yield. A di-oxan solution (25 mL) of pyridin-f-ol (0.95 g, 0.01mole) was added to a cooled solution of 4-phenyl-1, 2, 4-triazoline-3, 5-dione (1.75 g, 0.01 mole) indioxan (25 mL) at -\ 0°. The discharge of colourwas instantaneous, stirring of the reaction mixturewas continued for further Ii hr. The solvent wasthen removed under reduced pressure at tempera-ture below 40° till dryness. The solid obtained waschromatographed on a column of alumina usingchloroform-light petroleum (b.p. 60-80°) to giveafter recrystallisation from ethanol I(H)-5-phenyl-1, 3, 5, 7-tetrazatricyclo[5.3 .1.03.7] undeca-v-en-t,6, J I-trione 2 as yellow needles (1.83 g, yield68%), m.p. 280-300° with decomposition, IR: 3280(NH); 1780 and 1620 (C=O of the triazolidinedione ring), and 1690 cm-I (C=O, a, [3-unsaturated); 'H NMR: 8 5.5 (d, IH, H-2, hlO=1.5Hz 62 (dd IH, H-I0, J1o,2=1.5 Hz, J1o.9=5.5 Hz),69(dd, 1R H-9, J9,1O=5.5 Hz, J9.g=6 Hz), 5.8(d,IH, H-8, Js,9=6 Hz), 7.5-7,8 (rn, 5H, C6H5-)(Found: C, 58.12; H, 4.01; N, 20.25. C13HIO03 re-quires C, 57.77; H, 3.70; N, 20.74%); Mass: mlz242 [M+-N2].1-(4-Phenyl-l, 2, 4-triazolidin:l-yl)-5-phenyl-I, 3, 5, 7-tetrazatricy<:lo[5.3.1.03,7] undeca-9-en-4, 6, ll-trione 3. A dioxan solution (25 mL) ofpyridin-Svol (0.95 g, 0.01 mole) was added to acooled solution of 4-phenyl-l, 2, 4-triazoline-3, 5-dione (3 5 g, 0.02 mole) at -10° while stirring for1f2 hr. The solvent was removed under reducedpressure at 40°, whereupon a deep yellow solidwas obtained, and purified over a column of alu-mina using chloroform-light petroleum (60-80°)(3:1). A bright yellow solid gave after recrystalli-sation from ethanol 1-(4-phenyl-3, 5-dioxo-l, 2, 4-triaolidine-l-yl)-5-phenyl-l, 3, 5, 7-tetrazatricyclo-[5.3 .1.03,7]undeca-9-en-4,6, l l-trione 3, yield 3.15g,(71%), m.p. > 320° with decomposition. IR: 3300(NH), 1780, 1725 and 1765, 1715 (two doubletsfor the carbonyl absorptions of two triazalidine-dione rings), and 1690 cm-I (a, [3-unsaturated car-bonyl group); 'H NMR: 8 5.75 (d, 1H, H-2,J2,1O=1.0 Hz), 6.15 (dd, IH, H-I0, JIO,9=5.5 Hz,J102=1.0 Hz), 6.95 (dd, IH, H-9, Jg,9=5 Hz, AIO=6HZ'), 5.85 (d, lH, H-8, Jg,9=6 Hz) and 7.0-7.8 (m,10H, C6H5-) (Found: C, 56.25; H, 3.45; N, 22.28.C21H'5N705 requires C, 56.62; H, 3.37; N,22.02%); Mass: mlz 417 [M+-N2].1(H)-4-phenyl-l, 4-diazabicyclo [3.3.I]nona-7-en-3, 5, 9-trione 4. Sublimation of 2 (0.5 g,0.00185 mole) at 180° under reduced pressure (1.0mm Hg) in nitrogen atmosphere for 1f2 hr affordeda pale yellow solid on the cold finger (0.1 g, yield22%), m.p. 185-88°. IR: 3300 (NH), 1760, 1720(C=O of cyclic imide), 1680 crn") conjugated car-bonyl group); 'H NMR: 8 5.7 (d, IH, H-2, J2,g=1.5Hz), 5.95 (dd, IH, H-8,J8fI.5 Hz, J8,7=6 Hz), 5.45(d, IH, H-6, J6,7=5 Hz), 7.1 (dd, IH, H-7, J7,g=6Hz, J7,6=5 Hz), 6-7.8 (m, 5H, C6H5-) (Found: C,64.18; H, 4.49; N, 11.12. C1:HION203 requires C,64.46; H, 4.13; N, 11.57%); Mass: mlz 242 [M+].1-(4-Phenyl-3, 5-diono-l, 2, 4-triazolidine-l-yl)-4-phenyl-l, 4-diazabicydo[3.3.1] nona-7 -en-3, 5, 9-trione 5. Sublimation of 5 (1.0 g, 0.00239mole) at 180° under similar conditions as in thepreceding experiment afforded a yellow solid (0.35g, yield 37%), m.p. 220-22°. lR: 3320 (NH), 1775and 1718 and 1760 and 1720 cm-I (two doubletsfor two different cyclic imides); IH NMR: 85.8 (d,IH, H-2, J2,8=1.5 Hz), 5.9 (dd, IH, ~-8, J8,2=1.5Hz, J8,7=5.5 Hz), 5.75 (d, IH, H-6, J6,7=6 Hz), 7.00(dd, IH, H-7, J7,8=5 Hz, J7,6=6 Hz) and 7.6-7.8 (m,10H, C6H5-) (Found: C, 59.84; H, 3.22; N, 13.01.C21H'5N505 requires C, 60.13; H, 3.59; N,13.42%); Mass: mlz 417 [M+].ReferencesI Metzler D E & Snell E E, JOrg Chern, 77, 1977,234 I.2 Albert A & Phillips J N, JChern Soc, 1956, 1942,3 Mason S F, J Chern Soc, 1957, 5010.4 Sense P & Gallo G G, Ann Chime (Rome), 44, 1954,232.5 Baker W & Ollis W D, Quart Rev (London), II, 1957,15.438 INDIAN J CHEM, SEC.B, MAY 19986 Ramsden A, Adv Heterocycl Chem, 26, 1980, I.7 Dennis N, Katritzky A R & Takeuchi Y, Angew Chem,15, 1976, I and the references therein.8 Katritzky A R & Takeuchi Y, J Chem Soc, C, 1971, 847;878.9 Banerji J & Dennis N, Frank J, Katritzky A R & MatsuoT, J Chem Soc Perkin I, 1976, 2334.10 EI-Abbady S A, Al-Ahmady A A & Moustafa A H, IndianJChem, 31 B, 1992,24.II El-Abbady S A, Indian JHeterocyclic Chem, 3, 1993,25.12 Lutz 0, Ber, 43, 1910,2636.13 Acheson R M, Adv Heterocyclic Chem, 1,1963, 125.14 Baronet deBarry E, Cook J W & Driscoll E P, J ChemSoc, 123, 1923,503.15 Dennis N, Katritzky A R, Sabounji G J & Turker L, JChem Soc Perkin I, 1977, 1930.16 Dennis N, Ibrahim B, Katritzky A R, Taulov I G &Takeuchi Y, JChem Soc Perkin I, 1974, 1883.17 Dennis N, Ibrahim B & Katritzky A R, JChem Soc PerkinI, 1976, 2307.18 Entwistle N, Orbital Symmetry Correlation's in OrganicChemistry. A Guide to the Woodward-Hoffmann Rules,(Van No str. & Reinhold Co. London), 1972,33.19 Cookson R C, Gilani S S & I Steven's D R, J Chem Soc,(C) 1967, 1905.20 Anderson A B, JChem Phys, 62, 1975, 1187.21 Awad M K & Anderson A B, JAm Chem Soc, 112, 1990,1603.22 Schiott B, Hoffmann R, Awad M K & Anderson A B,Langmuir, 6, 1990,806.23 Abd-EI Halim S T & Awad M K, JPhys Chem, 97, 1993,3160.24 Awad M K, Khairou K S & Diab M A, Polym Deg Stab,46, 1994, 165.25 Awad M K, Polym Deg Stab, 69, 1995,33.26 El-Abbady S A & Awad M K, Polish J Chem, 69, 1995,33.27 Clementi & Raimondi D L, JChem Phys, 38, 1963,2680.28 Lotz W, JOpt Soc Am, 60, 1970,206.AppendixTheoretical MethodThe atom superposition and electron delocalization molecularorbital (ASED-MO) theory" is a semi-empirical theoreticalapproach for predicting structures, binding energies, reactionmechanism, and electronic and vibrational properties (cf. Refs21-26). It is based on partitioning the electronic charge dcen-sity into free atom parts and a component, owing to electrondelocalization bond formation. As the atoms are brought into amolecular configuration, the electrostatic forces on one nu-cleus of each pair are integrated by using the electrostatic theo-rem to yield a repulsive energy owing to rigid atom densitiesand attractive energy owing to electron delocalization. Thesum is, without approximation, the molecular binding energy.In the ASED-MO method, the atom superposition energy iscalculated using atomic densities, and electron delocalizationenergy approximated as the change in the total one-electronvalence orbital energy obtained by using a modified extendedHuckel Hamiltonian. The parameters consist of valence stateSlater orbital exponents" and ionization potentials'" (VSIP)for the consistent atoms. the atomic parameters are used for C,N, 0 and H (Table I). In all the reported results for equilibriumstructures, the bond lengths are variationally optimized to thenearest degree' In all the calculations the C-H bond lengthsare kept constants at 1.1oA.Table I-Atomic parameters used in the calculationsAtom s pna t:,a1.1681.1672.27222IP11.2612.0413.62Na IP t:,aC 2 16.59 1.658N 2 17.83 1.624o 2 28.48 2.246H 1 13.60 1.200(a) principle quantum numbers; (b) IP (eV); C Orbital expo-nents (au).

Enhanced reactivity of pyridin-3-o1 towards 4-phenyl-l, 2, 4-triazoline-3, 5- dione: FMO treatment of the cycloaddition process

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Enhanced reactivity of pyridin-3-o1 towards 4-phenyl-l, 2, 4-triazoline-3, 5- dione: FMO treatment of the cycloaddition process

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