Premium
A Rearrangement of 3‐Pyrazolines as a Missing Link
Author(s) -
Finke Jürgen A.,
Huisgen Rolf,
Temme Robert
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(20001220)83:12<3333::aid-hlca3333>3.0.co;2-j
Subject(s) - chemistry , aziridine , isoquinoline , ring (chemistry) , conjugated system , azomethine ylide , pyrazoline , stereochemistry , electrocyclic reaction , derivative (finance) , medicinal chemistry , cycloaddition , organic chemistry , financial economics , economics , catalysis , 1,3 dipolar cycloaddition , polymer
The thermal conversion of 4‐isoxazolines to 4‐oxazolines involves the transposition of two ring members. The ring‐contraction and ring‐expansion sequence in the reaction 2 → 5 has been previously clarified. The low N−N bond energy should favor an analogous conversion of 3‐pyrazolines 6 to 4‐imidazolines 7 ; the first example of such a transformation is reported here. In the yellow 16 , the 3‐pyrazoline is part of a pyrazolo[5,1‐ a ]isoquinoline system. Daylight induces a ring contraction, which affords the 2‐isoquinolylaziridine derivative 21 . The latter is converted at 65° to the tricyclic 4‐imidazoline 26 by a sequence of electrocyclic aziridine ring‐opening and 1,5‐electrocyclization of a C=N‐conjugated azomethine ylide 25 .