CONVERSION OF A 1,2,3-DITHIAZOLE INTO A 3H-PYRROLE-3-THIONE AND A 3H-PYRROL-3-YLIDENEPHOSPHORANE

Treatment of the readily available dicyanomethylenedithiazole 1 with e xcess of morpholine or triphenylphosphine gives the 3-azacyclopentadie nethione (3H-pyrrole-3-thione) 5 and the 3-azacyclopentadienylphosphor ane (3H-pyrrol-3-ylidenephosphorane) 16 respectively. Both products ar e deeply coloured and highly stabilised by extensive electron delocali sation: H-1 and C-13 NMR spectra show that rotation of the morpholine groups in 5 is hindered. Structure 16, the first azacyclopentadienylph osphorane reported, is proved by X-ray crystallography. Mechanisms are reported for these transformations in which the initial step is consi dered to be opening of the dithiazole ring of 1 by nucleophilic attack by the amine or the phosphine at the central heteroatom.