Abstract Treatment of di-and tetrabromo-1, 3-dithiole-2-ones 7 and 8 with Et 4 NI yields unsubstituted diene 4, trapped as its dimer or a cycloadduct; and dibromodiene 9. Treatment of 8 with DBU gives tribromodiene 10. Spectroscopic evidence indicates that tetramethylene- TTFs are formed by heating 9 and 10 with P (OEt) 3. Diels Alder adducts are formed by 9.