An efficient one-pot approach for the synthesis of fused triazolo 1,2,4-benzothiadiazine-1,1-dioxide derivatives from functionalised ynamides and sodium azide in the presence of CuI using PEG-400 as the medium is described. The cyclisation process involves intermolecular C–N bond formation and subsequent cycloaddition between ynamide and azide. Thus three new C–N bonds are formed in a single step. It is also demonstrated that the triazole ring in triazolo-1,2,4-benzothiadiazine-1,1-dioxide can be readily decyclised in the presence of glacial acetic acid with the elimination of molecular nitrogen.