Heterocyclic synthesis, from nitrilium

Heterocyclic diazo compounds, 8, 1 Heterocyclic ferrocenes, 13, 1 Heterocyclic pseudo bases, 1, 167 Heterocyclic syntheses, from nitrilium salts under acidic conditions, 6, 95 Hilbert—Johnson reaction of... 

In the case of the most reactive compounds, substitution at the carbon atom of diselenonium and ditelluronium dications is also a possible pathway. For example, formation of diselenide 117 from selenoxide 115 was explained by demethylation of intermediate dication 116 with trifluoroacetate anion.126 Dealkylation of salt 118, which is stable up to —20°C, leads to formation of nitrilium salt 119. The latter is transformed to amide 120 upon hydrolysis.64 Dealkylation of intermediate diselenonium dication 122 was suggested as the key step in the oxidative synthesis of 1,2,4-diselenazolidines 123 from eight-membered heterocycles 121 (Scheme 46).127... 

The assumption that the azomethine 34 is formed by an intermolecular hydride transfer from aldehyde 30 to the nitrilium salt 31 is not confirmed because the different Schiff bases 34 obtained carry the group R which are originated from the aldehyde 30. In this way, the process described in equation 14 can be reversed and applied as an enamide synthesis by acylation of imines2,3. However, the 7V-ethylbenzonitrilium salt 35 reacts with benzaldehyde to give the more stable Af-benzoyl-7V-ethyliminium ions 3647,49 which add to trimethylethylene to form 5,6-dihydro-4i/-l,3-oxazinium salt 37. On the other hand, the reaction of ions 36 with phenylacetylene leads to another type of 1,3-oxazinium heterocycle, namely to 4i/-l,3-oxazinium hexachloroantimonate 38 (equation 15). 

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