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Verallgemeinerung der Aminopentadienal‐Umlagerung
Author(s) -
Bacilieri Christian,
Reic Stefanie,
Neuenschwander Markus
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000607)83:6<1182::aid-hlca1182>3.0.co;2-t
Subject(s) - chemistry , nucleophile , delocalized electron , salt (chemistry) , formaldehyde , medicinal chemistry , generalization , stereochemistry , organic chemistry , catalysis , mathematical analysis , mathematics
Generalization of the Aminopentadienal Rearrangement Contrary to the rearrangement of 3‐amino‐3‐X‐prop‐2‐enals 2 (R=H), which easily give 3‐X‐prop‐2‐enamides 3 at low temperature, the postulated rearrangement ( Scheme 1 ) of the vinylogous 5‐amino‐5‐X‐penta‐2,4‐dienals 6 (R=H) normally stops at the level of 2‐aminopyrylium salts 7 . The main reason is that the charge in salts of type 7 is highly delocalized, leading to low‐energy species, which make addition of weak nucleophiles difficult. In this paper, two concepts for increasing the chances of the `aminopentadienal rearrangement' 6 →→ 8 are presented and substantiated by typical experiments. On one side, the easily available 2‐aminopyrylium chlorides 7 (X=Cl) are reacted with a twofold excess of secondary amines ( Scheme 2 ) to give 5‐(dialkylamino)penta‐2,4‐dienamides of type 9 and 10 . On the other hand, after replacing the amino groups of 6 by PhO and EtO groups, the corresponding 5‐chloro‐5‐phenoxy‐ ( 13b ) and 5‐chloro‐5‐ethoxypenta‐2,4‐dienals ( 13a ) easily rearrange at low temperature to give 5‐chloropenta‐2,4‐diene‐1‐carboxylates 18a and 18b , respectively, which are now obviously lower in energy than the corresponding pyrylium‐salt intermediates 16 ( Scheme 4 ).