Gas-phase conversion of tetrazoles to oxadiazoles: isolation and characterization of the N-acylated intermediate

The 5-substituted tetrazole ring was reacted in the gas phase with an acyl ion generated as the secondary reactive chemical ionization plasma in the m ass spectrometer. The product ions obtained, among others, were proposed as the rearranged 2,5-disubstituted-1,3,4-oxadiazole nucleus. Its structure w as demonstrated by comparison of the product ion spectrum of the 2,5-disubs tituted-1,3,4-oxadiazole derivative obtained by condensed-phase reaction an d the product ion spectrum of the oxadiazole derivative generated in sit-it by reaction of the 5-substituted tetrazole derivative with the acyl plasma . It was proposed that the mechanism of this transformation involved the pr esence of an acylated tetrazole intermediary, which could not be isolated i n the condensed phase, followed by the rearrangement, with nitrogen loss, t o afford the oxadiazole derivative. Under our conditions we were able to is olate the intermediate ion in the first field free region and demonstrate i ts structure by collision induced dissociation-tandem mass spectrometry. Co pyright (C) 2001 John Wiley & Sons, Ltd.