Uv spectra, 13 C chemical shifts, 1 H- 1 H coupling constants and relative stability of the four isomers are included.doi:10.1002/jhet.5570150203Jean DelettréRenée BallyJean-Paul MornonErmitas AlcaldeJavier De MendosaRobert FaureEmile-Jean VincentJosé ElgueroJournal of Heterocyclic Chemistry...