A2-1,2,3-Triazoline

Photodecomposition of A2-1,2,3-triazolines gives aziridines. In cyclohexane the cis derivative (434) gives the cis product (435), whereas photolysis in benzene in the presence of benzophenone as sensitizer gives the same ratio of cis- and /ran.y-aziridines from both triazolines which is accounted for in terms of a triplet excited state (70AHC(il)l). A2-Tetrazolines are photolyzed to diaziridines. 

The loss of CO, S, SO, S02 and N2 by thermolysis or photolysis has been used to make three- and four-membered rings for example, thiiranes (67) are obtained from (66) (CHEC 5.06.4.4). A2-1,2,3-Triazolines give aziridines and Wolff rearrangement of (68) gives (69). 

This article, which covers the literature up to 1983, endeavors to present a comprehensive, unified survey of the methods of synthesis and reactions of A2-1,2,3-triazolines. The chemistry of mono-, bi-, and polycyclic triazolines, as well as that of spiro- and bistriazolines, is considered. The 1,2,3-triazo-linones are not included, but a brief account of the chemistry of A3- and A4-1,2,3-triazolines is given.14... 

Triazolines show characteristic C—N absorption at approximately 1620 cm-1. In some instances, as in 1 -phenoxyphenyl-A2- 1,2,3-triazolines, the C—O—C band appears at 1250 cm-1.346 However, IR spectroscopy is mainly used to assign structures for triazoline decomposition products.197... 

The NMR spectra of the diene adducts show complex multiplets in the region characteristic for H4, 8 4.1-4.7 ppm, whereas the signals for H5 are displaced downfield to the H4 region because of the presence of the adjacent vinyl group.40 The cis and trans isomers of l-aryl-5-dialkylamino-A2-1,2,3-triazolines can be differentiated on the basis of their chemical shifts for H4, which appear at 8 4.21 and 8 4.54 ppm for the cis (54) and trans compounds (55), respectively.211 NMR techniques are thus conveniently used to follow cis-trans isomerizations.211... 

The chemical shifts for hydrogens and methyl groups at C-4 of 5-hydroxy-and 5-amino-A2-1,2,3-triazolines depend on the orientation relative to the hetero substituent at C-5. This has been extensively used for assignment of relative configurations at C-4 and C-5 of variously substituted A2-tria-zolines.216,259 lH-NMR spectra show that 5-alkoxy- and 5-hydroxy-A2-1,2,3-triazolines prefer an envelope conformation218 (63) with the hetero substituent at C-5 pseudoaxial at the flap and the N-l substituent pseudoequatorial, probably because of the anomeric effect. The cis and trans coupling constants in the 5-amino-, 5-hydroxy-, and 5-aIkoxy-A2-l,2,3-triazolines are very constant, being 7.0-9.8 and 2.0-3.4 Hz, respectively.218... 

The reaction of 1-azidoadamantane with ethyl acrylate affords exclusively a 4-substituted triazoline.155 The assigned regiochemistry is supported by 1H-and 13C-NMR spectra. The H-NMR spectral characteristics of the triazoline ring protons are similar to those reported for the corresponding adduct from phenyl azide.32, 3C-NMR spectra reveal a characteristic triplet at 8 61.9 assignable to C-5. 55 Different NMR techniques have been used in structure assignments of isoindolo[2,l-c]-A2-triazolines,324 spiroanthrone-triazolines,193,194 5-heteroaryl-substituted A2-1,2,3-triazolines,329 and some l-fluoro-(5-trifluoromethyl)-A2-l,2,3-triazolines.356... 

Some of the l-aryl-5-hydroxy-A2-l,2,3-triazolines with two different substituent groups at C-4 exist in solution as a mixture of the diastereomers they are readily interconvertible via a ketotriazene (59-62).259 The compositions of the equilibrium mixtures for a number of 1-methyl- and l-benzyl-5-hydroxy-A2-l,2,3-triazolines in solution were determined by NMR spectroscopy. The 8 values of the methyl groups at C-4 fall into two regions, namely at 81.41-1.57 or 1.05-1.21. They can be oriented either cis or trans relative to the hydroxy group at C-5. The compounds with bulky substituents at C-5 exist only in one form in which the bulky C-5 group is trans to the methyl group at C-4. The... 

Most known 1,2,3-triazoline chemistry is of the A2-compounds few studies concern the A3- and A4-compounds. In 1959, Mohr and Hertel first described several A4-1,2,3-triazoline intermediates.2 Despite a previous assignment of a A4-triazoIine structure for the phenyl azide-acrylonitrile... 

Aryl azides react with olefins to give 1,2,3-A2-triazolines.201-203 Whereas unactivated olefins are sluggish toward aryl azides, strained bicyclic systems, on the contrary, are particularly reactive.204-208 The rate of phenyl azide addition to a series of olefins parallels the heat of hydrogenation (Table Vffl).107 This thermodynamic parameter is a measure for the degree of strain associated with these molecules.200 Bicyclo[2.2.1]hep-tenes, such as norbomene (37), react readily at room temperature, and the addition occurs at the less hindered exo side (39).,06 1°7 210 211 A striking example of the increased... 

The cycloaddition of azides to multiple -ir-bonds is an old and widely used reaction. Organic azides are well known to behave as 1,3-dipoles in thermal cycloaddition reactions.178 The first example of this reaction was observed by Michael in 1893.179 Since then the addition of azide to carbon-carbon double and triple bonds has become the most important synthetic route to 1,2,3-triazoles, -triazolines and their derivatives.180-184 The cycloadditions of simple organic azides with electron-rich dipolarophiles are LUMO controlled.3 Since the larger terminal coefficients are on the unsubstituted nitrogen in the azide and unsubstituted terminus in the dipolarophiles, the 5-substituted A2-triazolines are favored, in agreement with experiment.185-187 Reactions with electron-deficient dipolarophiles are HOMO controlled, and... 

The first attempt to add diazomethane to a Schiff base was made by Meerwein,326 and the first successful addition was observed by Mustafa.327 Anils bearing nitro groups on the phenyl rings gave a cyclic adduct to which a 1,2,4-triazoline structure was assigned.327 A later reexamination of the reaction established the correct orientation of addition, and the products of the reaction of diazomethane with Schiff bases were assigned a A2-l,2,3-... 

The preparation and chemistry of organic azides have been intensively investigated since about 1960 because of their importance in preparative heterocyclic chemistry and as a source of nitrenes [1]. Many nitrogen-containing heterocycles such as carbazoles, furoxans, azepines, A2-triazolines, triazoles [2], tetrazoles [3], aziridines [4, 5], and azirines have been obtained by either the addition or the decomposition of azides. 

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