Tropylium azide

Other nice examples of well-studied solvent-dependent ionization equilibria of ionogens are azidocycloheptatriene tropylium azide [282, 283] and (triphenylcyclo-propen-l-yl) (4-nitrophenyl)malononitrile ("2a) triphenylcyclopropenium dicyano(4-nitrophenyl)methide (3a), the latter being one of the first examples of direct heterolysis of a weak carbon-carbon bond to a carbocation and carbanion in solution [284],... 

Analogous results have been obtained for the Lewis acid/base equilibrium between ionic tropylium azide and covalent 7-azidocycloheptatriene [178]. Again, in less polar solvents such as deuterio-trichloromethane and even [Dgjacetone, no ionization to give the tropylium and azide ions could be detected. Dipolar liquid sulfur dioxide, however, induces complete ionization at low temperature (—70 °C). 

A large number of sugars have been converted to azides that add smoothly to 4.3>3 and may be converted to other derivatives in high yield. Tropylium azide (43-5) is especially interesting in that the adducts can often be hydrolyzed quantitatively to the 1,2,3-triazole without a nitrogen substituent (Eq, 53). The compound 43-6 has also been prepared in fair... 

Figure 2. Exchange mechanisms for tropylium azide Reprinted with permission from Ref. 6. Copyright 1979, American Chemical Society.

Carbonyl Compounds. A convenient synthesis of tropone (52%) involves treatment of tropylium tetrafluoroborate with sodium azide to produce tropylium azide, followed by reaction with basic alumina. ... 

The structure of tropyl azide, which is synthesized by the action of azide ion on tropylium perchlorate , may be represented as the covalent azidocycloheptatriene (161), the non-benzenoid aromatic tropylium salt with azide as the counter-ion (162), or an equilibrium mixture of the two. Spectroscopic studies by Wulfman and colleagues indicate that in non-polar solvents such as carbon... 

With certain reactants isocyanides undergo three-component condensation and with others four-component condensation.32 1 Three-component addition occurs when isocyanides react with the combinations carboxylic acid-carbonyl compound, hydrogen, azide-carbonyl compound, tropylium salt-water, or two molecules of hydrogen thiocyanate. 

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