Vinylamine isomerization

PI1NH2 reacts with alkynes in the presence of HgO-BF, to give N-phenylalkylide-neamines arising from the isomerization of the initially formed vinylamines (Eq. 4.63) [258]. 

Despite the adequate accuracy ( + 6kJmol-1) for the calorimetrically derived enthalpies of formation of the isomeric AT-ethyl and A TV-dimethylanilines, we disappointedly acknowledge the absence of thermochemical data for the corresponding Af-ethyl and A N-dimethyl vinylamines. Indeed, we would have thought that enthalpy of formation data on the latter should be available from reaction calorimetry (cf References 34 and 40). More precisely, there is apparently no published account of the thermochemical analysis of the seemingly simple hydrolysis reaction... 

Primary enamines 115 have been obtained by flash thermolysis of adducts 116 at 600 °C in vacuo. A retro-Diels-Alder reaction occurs to give vinylamine (R = R1 = R2 = H). These primary enamines have been identified by their spectroscopic properties at — 80 °C. At temperatures > 80 °C isomerization to the imine occurs as well as self-condensation to various nitrogen heterocycles or acyclic azadienes. 

Upon UV irradiation, the heteroaromatic isoxazoles 35 rearrange similarly—most likely via azirines (293)159—to afford, by photocleavage of 293, nitrilylides (294)140,160 and finally the isomeric 1,3-oxazoles 295.1S7 However, ethyl 5-aminoisoxazole-4-carboxylate (34) isomerizes by another pathway. Similar to some thermal reactions,161 reorganization of the nitrile function in 295 affords the vinylamine 296157 (Scheme 80). Similar results are known for benzisoxazoles.162... 

In the reaction of N-disubstituted carboxylic acid amides with phosphorus pentachloride the corresponding iminium chlorides are formed, and again partially isomerization occurs in amides with a-hydrogens. For example, the iminium chloride XXIII and the vinylamine XXIV are formed in the reaction of disubstituted acetic acid diethylamides with phosphorus pentachloride ( 7,262 ... 

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