Synthesis and Properties of Novel Medium-sized Heterocyclic Compounds Containing Two Sulfur Atoms in the Ring and Synthetic Approaches to Conjugated Cyclic Disulfonium Ylides

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Tribenzo[b,f,h][1,4]dithiecin (8) was prepared by coupling 2,2'bis(bromomethyl)biphenyl ( 10) with 1,2-benzenedithiol (11) in the presence of NaH in acetonitrile.Another novel dithiecin derivative, 1,8-dihydro-2,7benzodithiecin (9) was synthesized by coupling of 1,4-dimercapto-2,3-Oisopropylidene-Lg-threitol (13a) with α,α'-dibromo-o-xylene (12), followed by hydrolysis and subsequent dehydration via the mesylate derivative (16).The benzodithiecin (9) was also prepared by treatment of dithiol (18) with butadiyne along with α,α'-bis(1-buten-3-ynylthio)-o-xylene (19) as a byproduct.Compound ( 19) was subjected to an intramolecular coupling reaction using CuClpyridine-O 2 in benzene to yield the 12-membered ring compound (23).We also describe our effort to prepare the corresponding cyclic diylide compounds from the above new dithiecins (8) and ( 9), and known dithiecin (7).In connection with our interest in heterocyclic conjugated (4n+2)π electron system, we have extensively investigated the chemistry of thiabenzenes 1 and azathiabenzenes. 2In the formers, sulfonium ylide bond forms part of a cyclic conjugated ring system containing six π-electrons.In the latters, sulfilimine bond forms part of a cyclic conjugated ring system.In continuing our study on the chemistry of cyclic sulfonium ylides, we planned to create a novel cyclic disulfonium ylide in which two sulfonium ylide moieties are incorporated in the (4n+2)π ring system.There is no paper on the synthesis and properties of cyclic diylides, although there have been described a few examples of the preparation of acyclic diylides containing two ylide structures in a given molecule.3In our previous paper we attempted the preparation of cyclic disulfonium ylide having a benzodithiazine skeleton (2) from disulfonium salt (1) by deprotonation with strong base, but our attempt resulted in vain to afford a demethylated sulfilimine (3) shown below.4 Thus, we planned to start with two sulfur atoms-containing ten-membered ring, dithiecin (4), in order to construct disulfonium ylides with 10 π-electrons (6) via the corresponding salt (5).In this paper, we describe the synthesis and some chemical properties of new dithiecins ( 8) and ( 9), and some approaches to the preparation of ten-membered disulfonium ylides from these new dithiecins and known dithiecin (7).5