Mesoionic compounds. 10. Preferred conformation of a 3-alkyl and 3-aryl-substituent in 4-unsubstituted and 4-acylated monocyclic munchnones and sydnones

A new 4-unsubstituted monocyclic oxazolium-5-olate (7c) was generated and N MR-characterized. Several 3-alkyl- and 3-aryl-4-acylated monocyclic munchno ne and sydnone derivatives were also prepared. From NMR experimental data a nd theoretical calculations different conformations were proposed for the 3 -alkyl group in munchnone- and sydnone series. The 3-arylated mesoionic oxa zolones presented non-planar structures.