1.2.4- Triazole 4-imines, cycloadditions

NMeTos, reacts with ammonia to give 1-methyl-1,2,4-triazole (577). Cycloaddition of thionitrosodimethylamine, Me2N—N=S, to the tetrazine ester (578) yields the triazole (579) with extrusion of nitrogen and sulphur.The formation of the triazolinones (580) from AT-phenylbenzonitrile imine (PhC=N—NPh) and aroyl azides involves a Curtius rearrangement of the latter to aryl isocyanates. 

Highly functionalized tetraaryl-4,5-dihydro-l,2,4-triazoles 118a-y have been prepared on a soluble polymer support (PEG4000) from the cycloaddition of diarylimines with a nitrile imine, prepared in situ from the arylhydra-zone 119. The triazole products are highly fluorescent and several have reasonable fluorescence quantum yields (Scheme 8 and Table 19) <2005S3535>. 

The reaction of phenylazoalkenes 424 with an excess of potassium thiocyanate in acetic acid produces the cycloadducts 425 that undergo further [3+2]-cycloaddition reaction with thiocyanic acid at the azomethine imine function giving rise to the bicyclic product imidazo[l,5-3][triazole]-2,5-dithiones 41 (Equation 87) <1998SL786>. 

The [3 + 2] cycloaddition of diazo compounds to imines or nitriles is an alternative approach to the preparation of 1,2,3-triazoles and 1,2,3-triazolines. For reviews, see CHEC-I <84CHEC-I(5)7I7>. 

Cycloadditions have been carried out to 37/-indoles (222, 223) (125,126), N-arylmaleimides (224) (127,128), l,2), -azaphospholes (225) (129), 5(47/)-oxazo-lones (226) (130), and 4,5-dihydrooxazoles (230) (131). The primary cycloadducts from the reaction of oxazolones (e.g., 226 with diaryl nitrile imines), derived from tetrazoles in refluxing anisole, do not survive. They appear to lose carbon dioxide and undergo a dimerization-fragmentation sequence to give the triazole 228 and the diarylethene 229 as the isolated products (130). In cases where the two aryl substituents on the oxazole are not the same, then, due to tautomerism, isomeric mixtures of products are obtained. 

The l,3,4-oxadiazin-6-one (240) undergoes cycloaddition followed by a remarkable rearrangement to give the triazole A(-imine 241 and an open-chain product (136). Cycloadditions have also been carried out with the following ring systems 1,2-dihydroisoquinoline (242) (137) dihydro-1,3-oxazine (243) (138,139), 2H-, 3-benzothiazine (244) (140,141), and 27/-l-pyran-2-thione (245) (142). 

Erba et al. (102) observed a novel formation of pyrrole imines 181 from the 1,3-dipolar cycloaddition of mtinchnones 179 and 5-amino-l-aryl-4,5-dihydro-4-methylene-1,2,3-triazoles 180 (Table 10.4). Treatment with benzaldehyde yielded 3-formylpyrroles (182). The reaction presumably involves loss of carbon dioxide, nitrogen, and morpholine from the initial cycloadduct. Unsymmetrical mtinchnones behave regioselectively and furnish products derived from bonding between C(2) of... 

J(P1)2797>. A similar cycloaddition-rearrangement sequence accounted for the formation of oxazolo[4,5-r/ [l,2,3]tri-azoles 203 as side products from the reaction between triazolium imides 201 and N-substituted benzaldimines, leading to the imidazo[4,5-t/ [l,2,3]triazole 204 (Equation 23) (see Section 10.05.10.3). The oxazolotriazoles 203 were presumed to arise as a consequence of hydrolysis of the imine to the parent aldehydes under the reaction conditions <2003ARK110>. 

Lactones of azocarboxylic acids are remarkably reactive. In the presence of phenyl isocyanate, the imino isocyanate formed from reactive 2-hydrazono-A3-l,3,4-oxadiazolines via a 1,3-dipolar cycloreversion is intercepted to give [l,2,4]triazolo[l,2-a]-[l,2,4]triazole-l,3,5-triones by means of two subsequent [2 + 3] cycloadditions via azomethine imine intermediates (Scheme 10) (76T2685). 

Sydnones can be regarded as cyclic azomethine imines and as such they undergo thermal cycloaddition reactions with a range of dipolarophiles. Thus, reaction with phenyl isocyanate converts 401 into 1,2,4-triazole 402. On photolysis, 3,4-diarylsydnones lose carbon dioxide and give nitrile imines, which can also be intercepted by dipolarophiles. Thermal reactions with acetylenic dipolarophiles lead to the formation of pyrazoles (Scheme 88) however, these reactions are rarely completely regioselective with unsymmetrical alkynes, e.g., <2000BKC761, 2000TL1687>. 

On the basis of the same principle, we developed a three-component synthesis of macrocycles starting from azido amide (46), aldehyde (47) and a-isocyanoaceta-mide (48) (the cx-isocyanoacetamides are easily available, see [84—86]) bearing a terminal triple bond (Scheme 11) [87]. The sequence is initiated by a nucleophilic addition of isonitrile carbon to the in situ generated imine 50 led to the nitrilium intermediate 51, which was in turn trapped by the amide oxygen to afford oxazole 52 (selected examples [88-94]). The oxazole 52, although isolable, was in situ converted to macrocycle 51 by an intramolecular [3+2] cycloaddition upon addition of Cul and diisopropylethylamine (DIPEA). In this MCR, the azido and alkyne functions were not directly involved in the three-component construction of oxazole, but reacted intramolecularly leading to macrocycle once the oxazole (52) was built up. The reaction created five chemical bonds with concurrent formation of one macrocycle, one oxazole and one triazole (Scheme 15). 

Dihydro-l, 2,3-triazoles were obtained by 1,3-cycloaddition of phenyl, 4-chlorophenyl, 4-bro-mophenyl, 4-nitrophenyl azides to acyclic and cyclic disubstituted alkenes48,66,67 and were successively decomposed to aziridines and/or imines at higher temperature66. If an intermediate temperature was chosen this permits the smooth elimination of nitrogen and the decomposition products were obtained directly68. 

Cycloaddition of aryl imines 155 with diazomethane followed by oxidation of the intermediate triazoline with potassium permanganate afforded l-(4-methylsulfonylphenyl)-5-ary 1-1,2,3-triazoles 156 <05JHC33>. l,2,3-Triazolo-3 -deoxycarbanucleosides and their analogs were prepared efficiently by palladium(0)-catalyzed reactions <05T11744>. Base-induced generation of aryl(l,2,3-triazol-lyl)carbenes from l-[(7V-phenylsulfonyl)benzohydrazonoyl)-... 

Simple 1,1-enediamines undergo 1,3-dipolar cycloaddition readily with 1,3-dipolar reagents. The 1,3-cycloadducts, which are stable and have been isolated in some cases, undergo further deamination by heating or in the presence of acid to give heteroaromatic products. This behavior resembles that of the parent enamines . Thus, 1,1-enediamines react with azides - and nitrile imines smoothly to give high yields of the cycloaddition products 217 and 219, and triazoles 218 and pyrazoles 220 after deamination (equations 89 and 90). 

Photochemically induced ring contraction of novel 4-iminodi-hydro-1,2,3-triazoles to the corresponding ( )- and (Z)-aziridin-imines has also been reported. A different pathway is followed in the 6-(l -triazolyl)uracils (24) which on irradiation in acetonitrile were converted into the pyrrolo[2,3-d]pyrimidines (25) via triplet biradical intermediates a novel cyclisation leading to the formation of pyrimido[4,5-c]isoquinolines is observed, however, when C-5 phenyl substituents are present on the triazole ring. Rate constants for the cycloaddition f diarylnitrilimines, generated by photoelimination of nitrogen from diaryl 2H-tetra-zoles, to various dipolarophiles have been determined experiment-... 

The reaction of N-aminoazonium salts with aliphatic and aromatic aldehydes in the absence of base gives the Schiff base type compounds 28.151,153-156 Some aliphatic ketones also react with N-aminoazonium salts.40,155 Hexane-2,5-dione reacts with N-aminopyridinium perchlorate to give l-(l -pyrrolyl)pyridinium cation 29 together with some of the bisper-chlorate 30.157 Certain esters such as diethyl malonate and ethyl cyano-acetate react with N-aminopyridinium salts in the presence of base to give the corresponding N-acylimines 31.48 However, the reaction of ethyl aceto-acetate and acetylacetone with N-aminoazonium salts in the presence of base gives 1,3-dipolar cycloaddition products (Section IV,C,1).36,154,158 The reaction of ethyl acetoacetate with 1-alkyl-l,2,4-triazole 4-imine affords zwitterionic triazolo[4,3-/>]pyridazines 32.139,159... 

Dipolar cycloaddition of 1-alkylbenzimidazole IV-imines with dimethyl acetylenedicarboxylate results in the formation of the ring-opened pyrazole derivative 79 (Eq. 31).151,203 1-Methyl-l,2,4-triazole 4-imine also reacts in a similar manner to give a pyrazole derivative (80),204 but Summers and Elguero obtained a rather unusual product (81) from the same reac-... 

Such rearomatization of the cycloaddition product in substituted A-imines is impossible without a considerable change of the molecular structure, and these compounds seldom undergo 1,3-dipolar cycloaddition, with the exception of pyridine,29 30 34 37 isoquinoline,29 30 and 1,2,3-triazole A-arylimines.97,106... 

Cycloaddition reactions of l,3,4-oxadiazin-6-ones 97 (R = Ph, R = Ar), via their 2,3-diaza-l,3-diene functionality, are observed by treatment with dipolarophiles. Thus, 2,5-diaryl-l,3,4-oxadiazines 97 react with diaryl nitrilimines 115, which are liberated in situ from the corresponding hydrazonoyl chlorides 114 and triethylamine, to give 1//-1,2,4-triazole A -imines 118 and open-chain products 119 <1996JHG591>. It is reasonable to conclude that intermediates 116 are formed initially from cycloaddition across the adjacent carbonyl-carbon nitrogen double bond and that subsequent CO abstraction gives 177-1,2,4-triazole A -imine derivatives 118. The open-chain adducts 119 are formed from intermediates 117, which result from the reaction of 115 at the carbonyl double bond of the oxadiazinones 97 (Scheme 15). 

T3506). Similarly, 2-halobenzaldehydes, isonitriles, amines, and propar-gylic acids underwent Ugi reaction, then copper(I)-catalyzed alkyne—azide 1,3-dipolar cycloaddition, and then intramolecular Ullmann-type triazole N-arylation to afford triazolo-flised benzodiazepines such as 136 (13EJ01223). Similar reactions involving a post-Ugi lactamization or a post-Ugi intramolecular imination process delivered benzo-l,4-diazepin-2,5-dione derivatives or 4,5-dihydro-3H-l,4-benzodiazepine derivatives (13ACO202,13T9056). 

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