N2 elimination

Tandem mass spectrometry (70eVEI) performed on 5-amino-l,3,4-thiadiazole-2-thiol 26 gave a weak abundance peak at m/z 78 Da (2%) corresponding to the [CH2S2]+ ion (Equation 1) <1999PCA5123>. The linked-scan spectra of the parent ion (M+) and the ion at mfz 106 showed that loss of HNC followed by N2 elimination accounted for the... 

Not much is known about the reactivity of the phosphinocarbene 2i. Problems arise, at least in part, from the high 1,3-dipolar reactivity of the diazo precursor li, which hides any carbene reactivity. Indeed, although li is stable in a toluene solution at 60°C for hours, the addition of an electron-poor olefin, such as a perfluoroalkyl-monosubstituted alkene, induces the exclusive formation of the thermodynamically more stable anti-isomer of the cyclopropane 14 (see Section V,B,3,a).36 This clearly demonstrates that the cyclopropanation reaction does not involve the carbene 2i, but that an initial [2 + 3]-cycloaddition occurs leading to the pyrazoline 13, which subsequently undergoes a classical N2 elimination.37... 

The attack of a nucleophile at Cl of the chain in an isolated pentatetraenylidene complex has been observed only once. The reaction of CH2N2 with trans-[Cl (PPr 3)2Rh=C=C=C=C=CPh2j proceeded by addition of CH2 to Cl, N2 elimination and rearrangement of the thus-formed diphenylhexapentaene ligand to form a C2,C3-bonded 6,6-diphenylhexapentaene complex (Scheme 3.36) [33]. 

Attempts to generate thiocamphor (5)-methylide (44) by the addition of diazomethane to thiocamphor and subsequent N2-elimination from the [3-1-21-cycloadduct 43 led to enethiol ether 45 via a 1,4-H shift (Scheme 5.17). The formation of an unstable intermediate 43 was proposed on the basis of the proton nuclear magnetic resonance ( H NMR) spectrum of the crude mixture. The postulated intermediate 44 could not be intercepted by dipolarophiles or methanol, and did not undergo electrocyclization to give the corresponding thirrane (41). 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

As shown in Scheme 8.67, the cyclization of diazoalkenes 273 requires thermal activation and not only affords 3/7-pyrazoles 274, but also cyclopropenes 275 that are formed from carbene intermediates (319). The activation parameters for cyclopropene formation (i.e., N2 elimination from 273) have been determined (320). A novel example involves the cyclization of the 3-nitro-l-diazoprop-2-ene derivative 276 into pyrazolopyridine derivative 277 (45). 

There are fewer documented examples of these N2-elimination reactions than might be expected. Aryldiazenido complexes are known to react with molecular hydrogen to yield arylhydrazine complexes via aryldiazene intermediates (equations 158 and 159). 

Keywords 4,6-dimethyl-1,2,3-triazine, enamine, Diels-Alder reaction, N2 elimination, microwave irradiation, pyridine derivative... 

Although thermal decomposition of 2-trityl-5-aryltetrazoles 197 occurs specifically, the final result of the reaction may be ambiguous. For instance, these compounds on heating in benzonitrile give 3,6-diaryl-l,3,4,5-tetrazines 198. Apparently the N2 elimination in a polar solvent (benzonitrile) occurs with cleavage of triphenylmethane followed by dimerization of the intermediate arylnitrile imine (Equation 19) <2002RJ01360>. 

Heating solutions of 5-aryloxy-l,2,3-thiadiazoles 82 (X = O) in DMF at 100 °C in the presence of excess sodium hydride afforded 1,4-benzoxathiins 84 (X = O). The transformation was proposed to proceed via initial cleavage of the thiadiazole ring with subsequent N2 elimination to give the intermediate 83. Subsequent intramolecular rearrangement of intermediates gave the 1,4-benzoxathiins 84 (X = O) <02H483>. 

The photochemical extrusion of nitrogen from cyclic azo compounds has been studied on a broad scale. Cyclic azo compounds, in contrast to acyclic ones can react with N2 elimination from both the Si and the T state. Ring strain as well as the lack of dsjtrans isomerisation favor photodecomposition. Since intersystem crossing is not very efficient the Ti state has mostly been populated by energy transfer. 

The photolysis in cyclohexane and cyclohexene+cyclohexane mixtures proceeds by N2 elimination. ... 

Chemical properties of silyl-, germyl-, and stannyl triazenes have not been studied very systematically so far. Most of the known compounds are air stable and sensitive to hydrolysis. Thermostability of triazenes of type 18a (R = organyl) is strikingly high, and these can often be heated above 150°C without decomposition. On the other hand, the known triazenes of type 18c (R = aryl) decompose slowly at room temperature. Triazenes of type 18b, 18d, and 18e are even more thermolabile and can be prepared only if triazene substituents are quite bulky [e.g., f-Bu3 SiN3H(Sir-Bu3) is stable above 150°C]. For more details of triazene thermolysis, which occurs mainly with N2 elimination, see Section II,C. 

Depending somewhat on the reactivity of the diazo component, the catalytic C-C coupling of eq. (3) is normally conducted at room temperature. To avoid early N2 elimination and unwanted side products, the reaction should be finished within several hours. 

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