4- - triazole-3,5-dione

Hydroxyhexahydropyridazine was freed from the polymer (168) by hydrolysis (Scheme 91) (79TL1333). Cyclic azo compounds may also be employed for example with 1,2,4-triazole-3,5-dione, adducts (169,170) are formed first and these are subsequently transfor-... 

Since both oxepin and its valence isomer benzene oxide contain a x-tb-diene structure they are prone to Diels-Alder addition reactions. The dienophiles 4-phenyl- and 4-methyl-4//-l,2,4-triazole-3,5-dione react with substituted oxepins at room temperature to give the 1 1 adducts 7 formed by addition to the diene structure of the respective benzene oxide.149 190,222... 

Occasionally, addition products of 4//-l,2,4-triazole-3,5-diones or diazenedicarboxylic esters and oxepins have been obtained whose formation can be rationalized by an addition to the 2,4-diene system in the oxepin, e.g. formation of 10.190191 In these cases, the primary adduct usually cannot be isolated, because it undergoes a hetero-Cope rearrangement to a tricyclic or bicyclic structure in which the oxepin oxygen has become part of a carbonyl function.190 191,227... 

Methyl-7-(trimethylsilyl)oxepin and 4-methyl-4//-l,2,4-triazole-3,5-dione as dienophile undergo a Diels-Alder reaction in which the 4,6-diene structure of the seven-membered ring react. Contrary to the aforementioned reactions, the primary adduct 12 is stable and does not rearrange to a carbonyl compound.222... 

Reduction of the 1//-1,2-benzodiazepines 6 with lithium aluminum hydride results in the dihydro compounds 8, which are dehydrogenated to the 3H-1,2-benzodiazepines 9 by 4-phenyl-4//-l,2,4-triazole-3,5-dione.123 The products readily revert to the 1//-tautomers in the presence of sodium methoxide. 3//-1,2-Benzodiazepines react with 3-chloroperoxybenzoic acid to give mixtures of 1- and 2-oxides, 10 and 11, in which the latter predominate. Treatment of the 2-oxides 11 with nucleophiles provides 3-substituted H- 1.2-benzodiazepines 12. Selected examples are given.124... 

The condensed l//-l,2-diazepines 12 are transformed into the 3//-tautomers 24 by reduction with lithium aluminum hydride to give 23, followed by dehydrogenation with 4-phenyl-4//-1,2,4-triazole-3,5-dione.146... 

Dihydroxypyridazines are readily prepared from the diene 103 and DEAZD or PTAD,159 and the amino acid 104, a constituent of the Monamycin antibiotics, was synthesized from the Diels-Alder adduct of phthalazine-l,4-dione and penta-2,4-dienoic acid.160 These unusual amino acids can also be synthesized from the PTAD and parent HTAD adducts of penta-2,4-dienoic acid,161 and a variety of similar adducts, triazolo-pyridazines 105, has been synthesized from a wide range of 4-substituted 1,2,4-triazole-3,5-diones.162... 

Bis-l,2,4-triazole-3,5-diones such as 110 have also been used in Diels-Alder reactions, and give bispyridazines.171 The pyridazine derivative 111 is formed in quantitative yield from PTAD and 2,7-dimethyl-2,3,5,6-octatetraene,172 and the azadiene, 4-aza-l,3,5-triphenylpenta-2,4-diene, also reacts readily with PTAD to give 112.173 There are many other examples of Diels-Alder additions of ADC compounds to simple acyclic dienes which proceed entirely as expected the above selection has been limited to reactions of synthetic potential and with novel features. 

Finally, the chiral l,2,4-triazole-3,5-dione (131) has been used to resolve chiral dienes such as 1,2,3-trimethylcyclooctatetraene.225... 

Because of its great reactivity PTAD has found wide use in the interception of reactive, unstable dienes. For example, unstable isoindenes,226 3a//-indenes,146 1,3-divinylallenes,227 and benzene oxides228 have all been successfully trapped with PTAD. 4-(4-Bromophenyl)-l,2,4-triazole-3,5-dione (5, R = 4-Br—C6H4) is often used if the derivatives ai e required for X-ray structure determination.229 Azodicarboxylic esters have been used to trap tetra(trifluoromethyl)cyclobutadiene,230 and spiro[4.4]nonatetraene.231... 

Several relevant papers and review articles have appeared recently. These contain reports on the mechanism and kinetics of the ene reaction of ADC compounds,243-245 examples of four-membered ring formation,246-247 other cycloadditions of ADC compounds,248-252 the synthesis of azoalkanes,253 the use of chiral l,2,4-triazole-3,5-diones,254 and the use of the DEAZD/PI13P reagent in organic synthesis.255... 

Another interesting synthesis of spiro[2.3]hexan-4-one (16) comprised of dipolar attack of 4-phenyl-l,2-dihydro-4//-l,2,4-triazole-3,5-dione on bicyclopropylidcnc to give a zwitterion 17, which underwent ring enlargement to 18 before ring closure to diaziridine 19 took place. Accordingly, in the presence of water, 18 was trapped with formation of spiro[2.3]hexan-4-one (16) which was also obtained from 19 by saponification.118... 

H-l,2,4-Triazole-3,5-dione, 4-phenyl- (8,9) (4233-33-4) tert-Butyl hypochlorite Hypochlorous acid, tert-butyl ester (8) Hypochlorous acid, 1,1-dimethylethyl ester (9) (507-40-4)... 

Iodobenzyl propargyl ether 57 cyclizes with 7t-allylpalladium (Scheme 18) to form after trapping by a secondary amine tetrahydro-2-benzoxepines 58 in 70% yield. The piperidino derivative 58 (R2 = (CH2)5) undergoes Diels-Alder reaction with 4-phenyl-l,2,4-triazole-3,5-dione as dienophile to give a spiro derivative 59 in 44% yield <1996TL6565>. 

The 3-vinylbenzofurans 174 and 175 reacted in the normal fashion with the highly reactive dienophile 4-phenyl-l,2,4-triazole-3,5-dione (PTAD)... 

As l,2,4-triazole-3,5-dione (PTAD) is a stronger dienophile than acetylenic esters, more facile formation of the Diels-Alder cycloadducts was expected. But because it cannot behave as a diene in a reaction with alkynes such as diethyl azodicarboxylate, the formation of dihydrooxadia-zines is excluded. In spite of these characteristics, no Diels-Alder adducts were obtained in the reaction of l-phenyl-4-vinylpyrazole with PTAD in acetone at -80°C and 2,2-dimethyl-4(l-phenylpyrazol-4-yl)-8-phenyl-l,6,8-triaza-3-oxabicyclo[4.3.0]nona-7,9-dione 277 was obtained as a major product. The isolation of the tetrahydrooxadiazine 277 indicates that the 1,4-dipole 278 was formed and trapped with acetone. 

Several syntheses of pyridazinopyridazines via Diels-Alder reactions of 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) (27) with functionalized dienes have been described. One example is the reaction of the diene (26) with PTAD (27) to afford the tandem Diels-Alder adduct (30) (Scheme 5) <85JCS(P1)71>. 

Triazolo-diazocine 12 was obtained through a [6+2] cycloaddition of cycloocta-l,3-dione and 4-pyren-l-yl-l,2,4-triazole-3,5-dione 80. Such a triazole derivative was obtained by in situ oxidation of l,2,4-triazolidine-3,5-dione 81, which was in turn obtained by reacting isocyanates and semicarbazides, followed by base-catalyzed cyclization... 

I, maleic anhydride II, 4-phenyl-[1,2,4]triazole-3,5-dione ill, norbornene iv, 2,3-dihydrofuran (xs) ... 

Aryl-l,l-difluorobuta-l,3-dienes (e.g., 35) react rapidly with 4-phenyl-4//-l,2.4-triazole-3.5-dione (36) in Diels-Alder reactions.88... 

Phenyl- and 4-methyl-4H-l,2,4-triazole-3,5-dione are often used as reactive dienophiles with subtituted norbornadienes and other polycyclic 1,4-dienes. 2-Trimethylsilyl-, 2-chloro-, 2-cyano- and 2-methoxycarbonylnorbornadiene react with 4-phenyl-4i/-l,2,4-triazole-3,5-dione in dichloromethane at room temperature to give the corresponding homo-Diels-Alder adducts 18, accompanied by [2 + 2] cycloaddition, rearrangement, insertion and polymerization products. 

Reaction of 4-phenyI-4/f-l,2,4-triazole-3,5-dione with bicyclo[2.2.2]octa-2,5-diene and bi-cyclo[3.2.2]nona-6,8-diene, carried out in acetone or dioxane, gave the expected homo-Diels-Alder adducts, which were used as starting materials for further syntheses. ... 

Cycloaddition Reactions of Dialkyl Azodicarboxylates and of 1,2,4-Triazole-3,5-diones... 

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