From tetrazoles via hydrazonoyl chlorides to 1,3,4-thiadiazole oligomers

5-Substituted tetrazoles react rapidly with Appel salt 1 at room temperature to give hydrazonoyl chlorides (14) in high yield. 5-Aminotetrazole reacts further to give an extended bis-imine (6) which, with triphenylphosphine at room temperature, rapidly gives 1,3,4-thiadiazoles 15 and 17. The mono-imines 14 react similarly to give simpler thiadiazoles 18 in high yield. By repetition of the tetrazole formation and Appel salt–triphenylphosphine sequence, these 2-cyanothiadiazoles 18 are converted in high yield into thiadiazole dimers and trimers 21, n=1 and 2. These reactions are explained mechanistically.