Spectrométrie de masse de triazolides et de leurs produits de transformation par pyrolyse‐éclair sous vide

Abstract

AbstractBesides the formation of acylium ions, the molecular ions of 1‐acyl‐1,2,4‐triazoles substituted (R) at position 3 lose competitively ketene and carbon monoxide after electron impact ionization, but the ketene loss dominates largely if R is a strong electron‐donating substituent. This supports the occurrence of an ion‐molecule complex which incorporates a substituted triazole and ionized ketene before the decarbonylation (methylene transfer) or the ketene elimination (hydrogen transfer).Flash‐vacuum pyrolysis (FVP) of these triazolides yields oxazoles with specific substitution at positions 2 (R) and 5 which implies an irreversible sigmatropic [1,5(1,2)] transformation. Oxazole formation dominates largely a competitive ketene loss if the triazolides bear a strong electron‐donating substituent like N(CH3)2; this kind of substitution does not however allow the migration of groups like CO2CH3 and CONH2 which have a lower migratory aptitude.The fragmentation of the ionized oxazoles is highly dependent upon the nature of the substituent at position 5 (methyl or phenyl) and is directed by ring cleavages, mainly of the 1,2‐bond. Moreover, compounds bearing a N(CH3)2 group undergo a complex rearrangement which eliminates (C, H3, N) from the molecular ions (for the oxazoles) or from the fragment ions [M‐C2H2O]−+ (for the azolides).