Reaction of bicyclic dienes with 4-substituted-1,2,4-triazoline-3,5-diones

Reaction of 1,2-dihydrophthalic anhydride and several of its imide derivatives, 1,2-dihydrophthalide and 1,2-dihydrophthalan with N-methyl- and N-phenyl-1,2,4-triazoline-3,5-dione affords two configurational families of adducts through attack from both possible directions. Major attack in the first three cases occurs mainly syn- to the hetero-ring but in the two latter cases anti- to it. These results may be explained by invoking stabilization of the transition state in the former cases through secondary orbital overlap and by simple steric effects in the latter.     

Propellanes—XXXVI : Reactions of bridged [10]annulenes with 4-substituted-1,2,4-triazoline-3,5-diones

1,6-Methano-, 1,6-oxa-, 1,6-imino- and 1,6-methylimino[10]annulene as well as several derivatives of the first-named compound react with 4-substituted-1,2,4-triazoline 3,5 diones to give mono- and/or bis-adducts. Attack apparently occurs from the side anti- to the bridging atom. Mass spectral results are reported for certain mixed di-adducts.     

Spontaneous alternating copolymerization of isobutoxyallene with 4-phenyl-1,2,4-triazoline-3,5-dione

The spontaneous copolymerization of isobutoxyallene ( 1 ) with 4-phenyl-1,2,4-triazoline-3,5-dione ( 2 ) was carried out to afford a copolymer with a number-average molecular weight of 5900–10,300. The copolymer consisted of a 2,3-polymerization unit of 1 and a  NN polymerization unit of 2 , maintaining an alternating character regardless of the monomer feed ratio. The corresponding copolymerization of 1 with 2 in the presence of methanol afforded the adduct of the compounds without the polymer, indicating the generation of a zwitterion of 1 and 2 . © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1564–1571, 2001     

Propellanes—XLIII: Inhibition of secondary orbital control in diels-alder reactions of certain propellanes with 4-substituted-1,2,4-triazoline-3,5-diones

A number of propellane substrates were prepared with special structural features, such that attack by dienophiles would be (a) from below—due to repulsive interactions, both electronic and steric, or (b) if the electronic influence from above was less efficient, than the attack would be from both directions. The predicted course of all the reactions has been realised experimentally.     

Low-temperature modification of dienic polymers via the “Ene” reaction with 4-substituted-1,2,4-triazoline-3,5-diones

4-Substituted-1,2,4-triazoline-3,5-diones have been used to synthesize a series of new polydienes by the “ene” reaction at ambient temperatures. The extent of chemical conversion can be varied widely and up to 93% of the diene-repeating units of the parent polymer chain undergo reaction. Yields of the new polymers based on the reactant range from 90 to 95% at room temperature; their physical properties range from secondary crosslinking effects or elasticity at low degrees of conversion to rigid, amorphous polymers with high softening points at high degrees of conversion. The new polymers show a predictable correlation between the extent of conversion and the softening point. A similar correlation exists between the polarity of the new polymers and the extent of conversion. Polydienes with conversions to the extent of 45% or greater are soluble in aqueous solutions of sodium hydroxide and those with conversions of 60% or greater are soluble in aqueous sodium bicarbonate. Thus, in general, the new polymers (1) have higher T_g, (2) become increasingly polar, hence are soluble in polar solvents, and (3) possess a reasonably acidic proton, hence form salts. Bistriazolinediones result in room temperature crosslinking. A kinetic study with model compounds suggests that the rate of the reaction can be varied, depending on the electronic nature of the 4-substituent.     

Diels-alder cycloadditions of N-substituted-1,2-dihydropyridines with 1,2,4-triazoline-3,5-diones and maleimides

The reaction of N-substituted-1,2-dihydropyridines 1 with 1,2,4-triazoline-3.5-diones 2 and maleimides 9 proceeds stereospecifically to afford endo cycloaddition products. N-Acetyl-1,2-dihydropyridines react with 2 to afford a stereo isomeric mixture of 3 and 4 whereas those possessing a N-ethoxycarbonyl, methoxycarbonyl, methanesulfonyl or benzenesulfonyl substituent yield 3 exclusively: similar results are also obtained in reactions employing maleimides. Stereochemistry was assigned on the basis of nmr data and use was made of the anisotropic effects of the 7,8 unsaturation on the R₁ and R₂ substituents.     

Polar hetero-Diels-Alder reactions of 4-alkenylthiazoles with 1,2,4-triazoline-3,5-diones: an experimental and computational study

The hetero-Diels-Alder reactions of 4-alkenylthiazoles with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) lead to new heteropolycyclic systems in excellent yields and high levels of stereocontrol through an exclusively suprafacial approach. 4-Alkenylthiazoles with a stereogenic center placed at the alkenylic substituent react with PTAD giving the corresponding chiral cycloadducts in moderate diastereomeric excesses. The stereochemical course is dominated by the steric interactions at the two diastereomeric transition states. A computational study of these processes with structurally simpler reagents has been carried out. A concerted pathway via a highly asynchronous transition state is preferred for 2-unsubstituted 4-vinyl and 4-styrylthiazoles. However, two alternative and equally likely pathways, concerted and stepwise, have been found to be followed by 2-methyl- or 2-phenyl-substituted 4-styrylthiazoles. The concerted pathway features a highly asynchronous transition state. For the stepwise pathway, the rate-determining step is the first one, as the energy barrier for the second step is virtually nonexistent.     

Photolysis of Matrix-Isolated 4-R-1,2,4-triazoline-3,5-diones: Identification of Aziridine-2,3-dione Transients

Matrix-isolated 4-methyl-1,2,4-triazolinedione 1a and 4-phenyl-1,2,4-triazolinedione 1b were photolyzed at lambda >/= 335 nm and lambda >/= 310 nm, respectively. The reactions induced by photolysis were monitored by FT-IR spectroscopy. The isocyanates 2a and 2b are always the more abundant products with carbon monoxide. Methyl- and phenylaziridine-2,3-diones (3a and 3b) were detected as minor, but well-identified reaction products. The IR experimental absorption bands were assigned by comparison with literature data and with simulated infrared spectra obtained by ab initio calculation at the 6-31G level. Stable at the matrix temperature (10 K), 3a and 3b photolyzed to isocyanates and CO when irradiated at lambda >/= 230 nm. Irradiation of 2b at this wavelength induces its decomposition. The kinetic data show that the rate constant process 1a --> 2a is faster than the 1a --> 3a process (3.29 x 10(-)(3 )and 2.35 x 10(-)(4)min(-)(1) respectively).     

Reactions of 4-phenyl-1,2,4-triazoline-3,5-dione with 2-pyrazolines

4-Phenyl-1,2,4-triazoline-3,5-dione (PTAD) acts as an efficient Michael acceptor in reactions with 1-unsubstituted 2-pyrazolines, giving substituted (3,5-dioxo-4-phenyl-1,2,4-triazol-idin-1-yl)-1-pyrazolines in quantitative yields. Through elimination of molecular nitrogen, the latter are easily transformed into the corresponding cyclopropanes. A reaction of methyl 5-methyl-2-pyrazoline-5-carboxylate with a twofold excess of PTAD leads to an intermediate bisadduct, which undergoes dediazotization to form a 1,3,5-triazabicyclo[3.3.0]octane-2,4-dione derivative. 1-Substituted 2-pyrazolines also add to PTAD with the exception that the 2-pyrazoline structure is retained in the product because of the migration of the C(3)H proton to PTAD.     

[4+2] Cycloaddition of 2(1H)-pyrazinones and 1,2,4-triazoline-3,5-diones

The reaction of 2(1H)-pyrazinones 1 and 1,2,4-triazoline-3,5-diones 3 was investigated by comparing that of 1 with singlet oxygen. 2(1H)-Pyrazinones 1 reacted in Diels-Alder fashion with 1,2,4-triazoline-3,5-diones 3 to afford [4+2]-adducts 4–17 in high yields.     

Mechanistic studies in the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with 2,5-dimethyl-2,4-hexadiene

Secondary isotope effect measurements of methanol adducts from the reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with 2,5-dimethyl-2,4-hexadiene, support the formation of an aziridinium imide intermediate rather than an open dipolar intermediate in the rate determining step.     

The oxidation of hydrazine derivatives with 4-phenyl-1,2,4-triazoline-3,5-dione

The oxidation of benzophenone hydrazone with 4-phenyl-1,2,4-triazoline-3,5-dione (PTD) yields benzophenone azine which is also formed from the reaction of the hydrazone with the ylid obtained from diphenyldiazomethane and PTD; the ylid forms a stable addition product with ethanol. With PTD, carbohydrazides are converted to 1,2-diacylhydrazines and small amounts of the corresponding azides; in contrast, p-toluenesulfonylhydrazine yields p-toluenesulfinic acid, isolated as its adduct with PTD, 1-(p-toluenesulfonyl)-4-phenylurazole. Possible mechanisms to rationalize the formation of these products are discussed.     

Propellanes—XLIV: Reaction of 11-substituted-1,6-methano[10]annulenes with 4-phenyl-1,2,4-triazoline-3,5-dione

Reaction of the bridged annulene derivatives and the dienophile mentioned in the title occurs through attack by the latter from below, anti- to the bridge. The mono-adducts obtained contain a substituted cyclopropane ring. Attempted nucleophilic displacement of suitable substituents was unsuccessful.     

Oxa-ene reaction of enols of amides with 4-phenyl-1,2,4-triazoline-3,5-dione

The reaction of 16 enols of amides with 4-phenyl-1,2,4-triazoline-1,3-dione gave open chain adducts rather than the [2 + 2] cycloadducts with a hemiaminal moiety, both in solid state and in solution. This assignment is based on X-ray crystallography, (1)H and (13)C NMR data, and IR spectra. The suggested mechanism involves hydroxyl proton loss in a formal oxa-ene reaction. Mechanistic details and a possible alternative are discussed.     

Synthesis and reactions of the Diels-Alder adduct of thebaine with 4-phenyl-1,2,4-triazoline-3,5-dione

The title compound was prepared. Upon treatment with HCl a rearrangement occurred and the “open” compound 5 was obtained as its colorless hydrochloride. This salt readily lost HCl and gave the betaine 5. The rearranged “closed” compound 6 was obtained from 5.Quaternary salts 13 and 14 may be formed in methanolic solution from thebaine and codeine and tetracyanoethylene. The salt 13 reacts with the title dienophile and affords the “open” adduct 15.     

Trapping of benzene oxide-oxepin and methyl-substituted derivatives with 4-phenyl- and 4-pentafluorophenyl-1,2,4-triazoline-3,5-dione

4-Phenyl-1,2,4-triazoline-3,5-dione and its pentafluoro analogue are efficient reagents for trapping arene oxides, e.g. benzene oxide-oxepin, affording crystalline adducts that can be quantitatively analysed by HPLC and MS techniques.