Synthesis and properties of novel medium-sized heterocyclic compounds containing two sulfur atoms in the ring and synthetic approaches to conjugated cyclic disulfonium ylides

Tribenzo[b,f,h][1,4]dithiecin (8) was prepared by coupling 2,2'-bis(bromome thyl)biphenyl (10) with 1,2-benzenedithiol (11) in the presence of NaH in a cetonitrile. Another novel dithiecin derivative, 1,8-dihydro-2,7-benzodithi ecin (9) was synthesized by coupling of 1,4-dimercapto-2,3-O-isopropylidene -Lg-threitol (13a) with alpha,alpha'-dibromo-o-xylene (12), followed by hyd rolysis and subsequent dehydration via the mesylate derivative (16). The be nzodithiecin (9) was also prepared by treatment of dithiol (18) with butadi yne along with alpha,alpha'-bis(1-buten-3-ynylthio)-o-xylene (19) as a bypr oduct. Compound (19) was subjected to an intramolecular coupling reaction u sing CuCl-pyridine-O-2 in benzene to yield the 12-membered ring compound (2 3). We also describe our effort to prepare the corresponding cyclic diylide compounds from the above new dithiecins (8) and (9), and known dithiecin ( 7).