The zinc(II) chloride catalysed reaction between ethylene trithiocarbonate
(1) and dibenzoylacetylene (3) gave the novel 2,3,5,6-tetrabenzoylthiopyran
-4-thione (4a) and its structure was elucidated by X-ray crystallography. T
reatment of 2,3,5,6-tetrabenzoylthiopyran-4-chalcogenones (4a,b) with triet
hyl phosphite afforded the bis-annelated furans 1,3,5,7-tetraphenylthiopyra
no[2,3-c:5,6-c']difuran-8-chalcogenones (5a,b) in almost quantitative yield
s. The mechanism for this furan formation is discussed.