Triazolium imides rearrangement

J(P1)2797>. A similar cycloaddition-rearrangement sequence accounted for the formation of oxazolo[4,5-r/ [l,2,3]tri-azoles 203 as side products from the reaction between triazolium imides 201 and N-substituted benzaldimines, leading to the imidazo[4,5-t/ [l,2,3]triazole 204 (Equation 23) (see Section 10.05.10.3). The oxazolotriazoles 203 were presumed to arise as a consequence of hydrolysis of the imine to the parent aldehydes under the reaction conditions <2003ARK110>. 

The synthesis of a new series of tetrahydro-oxazolo[4,5-d]-1,2,3-triazoles (102) has been reported. The triazolium imide 1,3-dipole (104) reacted with ( )-cinnamaldehyde in refluxing ethyl methyl ketone. It is significant that it was to the C=0 bond of the a,/ -unsaturated aldehyde that the cycloaddition took place, yet analogous addition to benzaldehyde or aliphatic ketones was not possible. The primary products of the cycloaddition reaction (105) underwent a sigmatropic rearrangement to furnish the new ring system (102) as shown in Scheme 23 <90JCS(P1)2527>. 

Dihydro-1,2,3,5-tetrazines (13) have been obtained by 1,3-dipolar cycloadditions of A-sul-finylimines with substituted triazolium imides (27), followed by rearrangement and sulfinylimine elimination. When Ar Ar, both expected products (13a) and (13b) were produced (Scheme 4) <88CC232, 90JCS(P1)2527>. 

The reactions of 1,2,3-triazolium 1-imide (277) with a range of alkene and alkyne dipolarophiles give rise to a variety of new ring systems (Scheme 54). Compounds (276) and (278) are obtained from (277) by reaction with acrylonitrile and DMAD, respectively. These reactions are tandem 1,3-dipolar (endo) cycloadditions and sigmatropic rearrangements which are regio- and stereospecific <90JCS(Pl)2537>. Kinetic and mechanistic studies show that these reactions are dipole-HOMO controlled. The second-order rate constants are insensitive to solvent polarity, the reaction indicates... 

---