ON THE REACTION OF 1-AZA-2-AZONIAALLENE SALTS WITH ACETYLENES

1-Aza-2-azoniaallene cations 3, prepared in situ from geminal chloro(a lkylazo) compounds 2, react with acetylenes 4 to give either 1H-pyrazo lium salts 6 or 4H-pyrazolium salts 7 or mixtures of both. 4H-Pyrazoli um salts with a hydrogen atom attached to C(4) rearrange to the proton ated 1H-pyrazoles 8, from which the free bases 9 are obtained upon tre atment with aqueous NaOH. According to AM1 calculations the cycloaddit ion of acetylenes to 1-aza-2-azoniaallene cations is a concerted proce ss, which can be classified as a ''1,3-dipolar cycloaddition with reve rse electron demand''. The cycloaddition forming the intermediates 5 i s followed by an [1,2] alkyl shift to furnish the final products 6-8. The direction of the [1,2] shift has been found to be governed by subt le steric effects.