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Photochemische Cycloadditionen von 3‐phenyl‐2 h ‐azirinen mit Aldehyden. 31. Mitteilung über Photoreaktionen
Author(s) -
Giezendanner Heinz,
Heimgartner Heinz,
Jackson Barry,
Winkler Tammo,
Hansen HansJürgen,
Schmid Hans
Publication year - 1973
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/hlca.19730560745
Subject(s) - chemistry , stereoselectivity , nitrile , cycloaddition , condensation , medicinal chemistry , stereochemistry , organic chemistry , catalysis , physics , thermodynamics
Experiments concerning the photochemical condensation of 3‐phenyl‐2 H ‐azirines 1 with aliphatic and aromatic aldehydes to 3‐oxazolines 4 are fully described ( cf . scheme 1 ). Photochemically nitrile methylides of type 2 are first formed, which then very quickly react thermally with the aldehydes in a regiospecific manner to give the 3‐oxazolines 4 . Azirines monosubstituted in position 2 (l b and 1 c ) give mixtures of cis , trans ‐oxazoline isomers, in which the cis isomer predominates. The stereoselectivity of the cycloaddition reaction can be rationalized by a simple model (scheme 10). The stereoisomeric 3‐oxazolines 4 are distinguishable in the NMR. spectra by the large homoallylic coupling constants between the H atoms on C(2) and C(5).