Säure‐Additionen an ‘Push‐Pull’‐Enine. Erste Beobachtung einer Umlagerung von 5‐Chloro‐5‐(dialkylamino)pentadienalen

Reaction of ‘Push‐Pull’ Enynes with Acids. First Observation of a Rearrangement of 5‐Chloro‐5‐(dialkylamino)pentadienals ‘Push‐pull’‐enynes 7 react easily with HCl as well as with AcOH to give 5‐amino‐5‐chloropentadienals 8 and 5‐(acetoxy)‐5‐aminopentadienals 13 as well as the corresponding ketones. In view of a postulated rearrangement of compounds 8 and 13 ( Scheme 2 ), both types of compounds have been treated with traces of acid. While no definite reaction is observed in case of 13 , HCl‐addition products 8 easily and quantitatively rearrange to give 2 H ‐pyran‐2‐iminium chlorides 10 which are the postulated intermediates of the rearrangement 8 → 12 ( Scheme 2 ).