The synthesis of a series of unprecedented tricyclic heterocycles, 1,2,4-tr
iazolo[3,2-d][1,5]benzothiazepine 6-oxides (5a-i), was accomplished via cyc
loaddition of the allene-like cations 3, derived from thiochroman-4-one ary
lhydrazones, to the triple bond of nitriles and ensuing rings expansion ann
ulation. The structure of one product (5h) has been unambiguously determine
d by X-ray diffraction analysis.