1,2,4-Triazolin, 4-phenyl-3.5-dione

Reactions of Allylstannanes With 4-Phenyl-l, 4-Triazoline-3 -Dione and Diethyl Azodicarboxylate... 

Dihydropyridines 8 react with dienophiles such as A -phenyl maleimide (2) and l,2,4-triazoline-3,5-dione 9 to give the Diels-Alder adducts 10 and 11, respectively (76JHC481). Fowler observed that when a mixture of 1,2- and 1,4-dihydropyridines was treated with maleic anhydride (12), only 1,2-dihydro-pyridines yielded the Diels-Alder adducts 13, whereas the 1,4-dihydropyridines showed no reactivity with 12 (72JOC1321) (Scheme 1). 

Preparation of cholesta-5,7-diene-ia,3/3-diol a solution of 500 mg of the 1,4-cyclized adduct of cholesta-5,7-dien-3/3-ol-ia,2a-epoxideand 4-phenyl-1,2,4-triazoline-3,5-dione in 40 ml of tetrahydrofuran is added dropwise under agitation to a solution of 600 mg of lithium aluminum hydride in 30 ml of THF. Then, the reaction mixture liquid Is gently refluxed and boiled for 1 hour and cooled, and a saturated aqueous solution of sodium sulfate is added to the reaction mixture to decompose excessive lithium aluminum hydride. The organic solvent layer is separated and dried, and the solvent Is distilled. The residue Is purified by chromatography using a column packed with silica gel. Fractions eluted with ether-hexane (7 3 v/v) are collected, and recrystallization from the methanol gives 400 mg of cholesta-5,7-diene-la, 3/3-diol. 

The product 18 does not give a Diels Alder adduct with 4-phenyl-l,2,4-triazoline-3,5-dione, indicating the absence of its bicyclic tautomer. 

An example of a /zctcro-Diels-Alder reaction in SC-CO2 is the cycloaddition of anthracene with 4-phenyl-1,2,4-triazoline-3,5-dione, carried out at 40 °C and at a pressures between 75 and 216 bar [86]. The rate constant increases with decreasing pressure and the highest reactivity was observed at the critical pressure. The value of the rate constant at the critical pressure was higher than that observed in liquid CHCI3 and MeCN at the same temperature. At higher pressures, the rate is slower than that in the polar solvents, which reflects the apolar nature of SC-CO2 as a solvent. 

In order to smdy the effect of perturbation arising from spiro-conjugation on the chemical reactivities, in particular the facial selectivities, sterically unbiased dienes (96 and 97) based on fluorenes in spiro geometry have been synthesized [165]. These dienes react as Diels-Alder dienes with several dienophiles (maleic anhydride (MA), A-phenylmaleimide (PMI), A-phenyl-l,3,5-triazoUne-2,4-dione (PTD) and iV-methyl-l,3,5-triazoline-2,4-dione (MTD)). 

The values of X = NH, OH, F, Cl, and CH3 are smaller than that of X = H, in accordance with the observed selectivity. Excellent correlation was found for all other cyclopentadienes described above. Syn rr-facial selectivity in the reactions between 4-phenyl-l,2,4-triazoline-3,5-dione and cyclopentadiene having simple alkyl group at 5 positions are reported by Burnell and coworkers [46] (Scheme 37). 

In 1974, Vogel and his coworkers62) reported the first synthesis of the syn-benzene bisepisulfide 119 and its thermal behavior. The bisepisulfide 119 is thermola-bile and decomposes at 20 °C with a half-life of about 30 min to form benzene and sulfur as final products. When the reaction was carried out in the presence of 4-phenyl-1,2,4-triazoline-3,5-dione (PTD), 119 gave the product 120 which corres-... 

Dipolar cycloaddition of pyrido[2,l-A][l,3]thiazinium betaine 507 (R = Me) with 1-diethylamino-l-propyne afforded cycloadduct 508, from which quinolizin-4-one 509 formed by a rapid cheletropic extrusion of COS (Scheme 53) <1995T6651>. 1,4-Dipolar cycloaddition of 507 and 4-phenyl-l,2,4-triazoline-3,5-dione yielded 511 (via 510) <1995H(41)1631> and 512 <1995T6651>. 

Methyl-3-(tetramethylcyc opropylidene)propene (176), obtained by isomerization of allene 175 with potassium ferr-butoxide, added to 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD, 177) at room temperature to give the Diels-Alder adduct 178 in 46% yield (Scheme 26) [43]. 

Electrocyclic reactions have been performed with three of the bridged [ 11 Jan-nulenones. Both 11 and 13, which both contain a cycloheptatriene unit, undergo Diels-Alder additions with dienophiles via their norcaradiene valence tautomers 41 and 43 and yield adducts of the type 42 and 44. Annulenone 13 was found to react only with 4-phenyl-l,2,4-triazoline-3,5-dione whilst 11 underwent reaction with a variety of dienophiles. 3,8-Methano[ 11 Jannulenone 12 contains a tetraene system and undergoes addition reactions, apparently of the (8 + 2)-type, at the termini of the tetraene system. Thus with maleic anhydride the adduct 46, the valence tautomer of the initial adduct 45, was isolated. 

Gycloaddition reactions of betaine 64 with electron-deficient dipolarophiles, such as the extremely reactive 4-phenyl-1,2,4-triazoline-3,5-dione, gave the corresponding cycloadduct 65 isolated in quantitative yield (Equation 8) <1995T6651>. 

The attack from the less-hindered side and in which how the products formed by exo or endo additions vary has attracted great attention and a very interesting case of the reaction between naphthalene derivatives and 4 phenyl-1, 2, 4 triazoline 3, 5 dione (d) acting as dienophile has been reported by B.M. Jacobson in 1973. 

The most powerful azo dienophile is the cisoid 4-phenyl-l,2,4-triazoline-3,5-dione 264, which is surpassed in reactivity only by singlet oxygen. The dione adds rapidly to all types of dienes and the process can be followed visually since the bright-red color of the reagent is discharged when the reaction is complete136. 

The (diphenylmethylene)aminocyclobutenecarboxylates 109 obtained by rearrangement of the DMPA-H adducts of 1-Me, 2-Me, contain a 2-azadiene unit and a cyclobutene moiety. Indeed, the parent compound 109 a reacted with 4-phenyl-l,2,4-triazoline-3,5-dione (PTAD, [80]) at room temperature in a [4-1-2] cycloaddition mode to yield the tricyclic tetraazaundecene 132 in almost quantitative yield (Scheme 44) [8]. As substituted cyclobutenes, compounds 109 should be capable of opening up to the corresponding butadienes [1, 2b, 811. When compounds 109 were subjected to flash vacuum pyrolysis, the dihydro-isoquinolines 135 were obtained, presumably via the expected ring-opened intermediates 133, which subsequently underwent bn electrocyclization followed by a 1,5-shift, as is common for other 3-aza-l,3,5-hexatrienes [82]. 

C. Heteroatomic dienophiles 111 Esters of azodicarboxylic acid 12k 4-Phenyl-l,2,4-triazoline-3,5-dione 131 hninocarbamates... 

Phenyl-l,2,4-triazoline-3,5-dione has been prepared by oxidizing 4-phenylurazole with lead dioxide,7 and with ammoni-acal silver nitrate followed by an ethereal solution of iodine.8 The yields are low for both methods. 4-Substituted triazoline-diones can also be made by oxidation of the corresponding urazole with fuming nitric acid9 or dinitrogen tetroxide.10 Oxidation by <-butyl hypochlorite in acetone solution has also been described 1112 it, however, yields an unstable product, even after sublimation. Either dioxane12 or ethyl acetate are preferred as solvents for the reaction, since the product is obtained in a stable form. The latter solvent is superior since... 

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