S-Tetrazine

Figure 9.46 Rotational structure of the Ojj bands in the fluorescence excitation spectra of s-tetrazine dimers at about 552 run. Bottom Ojj band of planar dimer. Middle Ojj band of T-shaped dimer with transition in monomer unit in stem of T. Top Ojj band of T-shaped dimer with transition in monomer unit in top of T. (Reproduced, with permission, from Haynam, C. A., Brumbaugh, D. V and Levy, D. H., J. Chem. Phys., 79, f58f, f983)...

C2F12C12F2 (1,2-dichloro-l, 2-difluoroethane) symmetry elements, 83 CF13C3CN (methyl cyanoacetylene) interstellar, 120 2142X4 (s-tetrazine) fl S3 — X Ag transition, 3971F F1COOCF13 (methyl formate) interstellar, 120... 

X4)2 (s-tetrazine dimer) electronic spectrum, 397tf... 

Bromo-6-phenyl-s-tetrazine (334) gives the 3-hydroxy analog in quantitative yield after a few minutes at 95° in ethanolic potassium hydroxide or ethanolic ethoxide. As with other highly activated alkoxy-azines (cf. Section III,B,4,c and reference 582), the latter... 

The electron-deficient nature of the s-tetrazine ring-carbons is indicated by formation of a dipotassium salt (C2N4K2) of tetrazine in liquid ammonia, by easy decarboxylation of the 3,6-dicarboxylic acid (335), and by the very weak basicity of the 3,6-diamine (336). 

The preparation of rigid alicyclic molecules bearing effector groups from alkene blocks using s-tetrazines and 1,3,4-triazines as stereoselective coupling agents [67]... 

S-Tetrazin. Das bei der Reaktion von s-Triazin und Hydrazin entstehende i. 2-Diformylhydrazin-dihydrazon (XLIV) ist eine... 

Bertinotti, F., G. Giacomello, and A. M. Liquori. 1956. The Structure of Heterocyclic Compounds Containing Nitrogen. I. Crystal and Molecular Structure of s-Tetrazine. Acta Cryst. 9, 510. 

Two oxadisilole-fused benzo[c]furans illustrated below were prepared making use of Warrener s tetrazine protocol <06JOC3512>. Their reactivities, photophysical, redox and thermal properties were all assessed. As shown below, an isocorannulenofuran was also synthesized, again by employing Warrener s route, from readily accessible bromocorannulene <060L5909>. 

Another convenient entry to fused cyclobutene-1,2-diesters was via site selective modification of the norbomene rt-bond in Smith s fe-alkene 49, e.g. treatment with 3,6-di(2 -pyridyl)-s-tetrazine 51 followed by DDQ oxidation afforded the cyclobutene-derivative 53 <97AA119>, while direct coupling with 3,5-f> (trifluoromethyl)-l,3,4-oxadiazo]e 54 furnished the tas(cyclobutene-l,2-diester) 55 (Scheme 6) <97SL196>. 

The generation and trapping of 5,6-bis(trimethylsilyl)benzo[c]furan 126 was reported by Wong utilizing Warrener s s-tetrazine methodology. The trapping of the silylated isobenzofuran with A-phenylmaleimide is illustrated below. A number of other dienophiles such as dimethyl acetylenedicarboxylate, benzoquinone, naphthoquinone and anthra-l,4-quinone have also been used <00TL5957>. 

Thus, azines, with the exception of possibly s-tetrazine (39), have similar resonance energies (Table VII). Even though the 7r-density is concentrated... 

Relatively low RE values, compared to that of benzene, of pyridazine, s-triazine, and s-tetrazine (see Table VII) are explained, primarily, by changes in the cr-system that occur in passing from the conjugated system to the reference system, i.e., by the factors, such as the compression energy, that were noted in the discussion of the so-called empirical resonance energies. 

Like hexazine, s-tetrazine (39) and pentazine (40) are thermodynamically unstable to decomposition into HCN and N2 (see Table VII). 

Di ami nodi hydro-s-tetrazine, C2H5N5 mw 114.12, N 23-65%. The 3,6,-Diamino-1-4-dibydro s-1 etrazin e,... 

Diamino-3,6-di hydro-s-tetrazine Dini-trate (called Nitrate de diaminot trazene in Fr),... 

We performed a series of theoretical studies on pump-probe diffraction patterns with a twofold objective the first aim is to evaluate the effect of electronic and vibrational excitation on electron diffraction patterns, compared to that of structural rearrangements that are the primary goal for observation in structural dynamics measurements. Secondly, we wish to explore to what extent electronic and vibrational probability density distributions are observable using the pump-probe electron diffraction methodology. Previously we have discussed the effect of electronic excitation in atomic systems,[3] and the observability of vibrational excitation in diatomic and triatomic systems.[4,5] We have now extended this work to the 8-atomic molecule s-tetrazine (C2H2N4). 

In the simulations presented here, we assume that a pump laser excites the molecule to either the vibrationless, or specific vibrational levels of the Si electronic state. The diffraction pattern is measured by scattering the electron beam off the excited molecules on a time scale shorter than the rotational motion of the molecules, i.e. on a time scale less than about 10 ps. The diffraction pattern is measured in the plane perpendicular to the electron beam. The diffraction patterns shown here are for an excitation laser polarization parallel to the detector plane, and perpendicular to the electron beam. Since the electronic transition dipole moment of s-tetrazine is perpendicular to the aromatic ring, this pump-pulse polarization selects preferentially those molecules that are aligned with the aromatic plane parallel to the electron beam. 

Fig. 3. Difference diffraction pattern of s-tetrazine, between the vibrationless levels of the S, and the S0 electronic states, respectively.

Fig. 26. Conformational sets and types of hexahydro-s-tetrazines. (Reprinted with permission from Ref. 374. Copyright 1976 American Chemical Society.)...

It has been pointed out88 that the angle —in pyrimidines is about 11° less than the angle —C—. Also, in -triazine, C8N Ha, which is a planar molecule with trigonal symmetry, the two angles have the Values84 113.2° 0.4° and 126.8° 0.4°, respectively, with difference — 13.6°, and in s-tetrazine, they have the values81... 

Pyrrolidinobenzo[6]furan (228) can function as a dienophile and by inverse electron demand it forms the [4 + 2] adduct (291 70%) with 1,4-diphenyl-s-tetrazine. With DMAD a [2 + 2] adduct (292) is formed which is easily converted into the benzoxepin (293) on heating (74RTC321). 

A new potential synthesis of anthraquinones based on l-acetoxybenzo[c]furan (470) has been reported. The s-tetrazine reaction used to generate the benzo[c]furan proceeded in the presence of N-methylmaleimide to give the expected adduct (471). The reaction takes a different path in the presence of quinones to yield a novel phthalide (472), the structure of which was confirmed by X-ray diffraction (81AJC1223). 

Of the three possible tetrazine systems the 1,2,4,5-tetrazines, also called s-tetrazines or sym- tetrazines, are by far the best known class. The parent compound of the 1,2,4,5-tetrazine series has structure (38) and is numbered as indicated. It was prepared for the first time by Hantzsch and Lehmann in 1900 (00CB3668). The two Kekule structures for (38) are degenerate, as was confirmed by X-ray crystallographic analysis. 

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