Dibenzo-1,2-dithiin

In wet acetonitrile, the oxidation of diaryldisuUrdes [119] and dialkyl disulfides (Aik 7 f-Bu) [120] affords the corresponding aryl and alkylthiosulfonates in good synthetic yields (Eq. 15). Thus, the oxidation of a cyclic disulfide, dibenzo(c,e)-1,2-dithiin (1,1) does not affect the S—S bond and results in a corresponding thiosulfonate, dibenzo(c,e)-l,2-dithiin-l,l-dioxide(Scheme 27) [121]. Such oxidized products can form in wet acetonitrile as well as in a dry solvent, but in the latter case this is probably a result of disproportionation of the primarily... 

Thianthrene is numbered as shown in 1 using current Chemical Abstracts numbering before 1937, the numbering shown in 2 was used in Chemical Abstracts. The ring positions ortho to sulfur have been termed a, and the others are termed y3. Alternative names for thianthrene, found more in older literature, are dibenzo-1,4-dithiadiene, dibenzo-1,4-dithiin, di-o-phenylene sulfide, and diphenylene disulfide. The literature also contains references to o-thianthrene this is dibenzo[c,e][l,2]dithiin, (3). 

Mass spectra of the dibenzo-l,2-dithiins 52 and S3 display intense parent ions, indicating that loss of an electron gives rise to particularly stable radical cations <2000JA5052>. 

The synthetic procedure to create the dibenzo[l,2]dithiin derivative 237 (Scheme 67) with a well-defined chromo-phore and also electroactive under mild conditions has been published <2006TL9135> the disulfide bridge proved electrochemically switchable. 

The UV photoelectron spectra of 1,4-dioxin, 1,4-dithiin, 1,4-oxathiin, and their dibenzo derivatives as well as the saturated compounds were detailed in CHEC(1984) <1984CHEC(3)958>. 

There are few examples of the preparations of heterocyclic compounds containing two or more heteroatoms which involve cyclization with formation of a bond between two heteroatoms. The best known instances of this type of reaction, all of which are [6 + 0] reactions, are the preparations of benzocinnolines as outlined in equations (l)-(4). A similar type of approach to that outlined in equation (4) has been used for the direct preparation of the di-N-oxide (2) from the dioxime (1 equation 5). The naphthotriazine betaine (4) is obtained as one of the products of the thermal decomposition of the azidoazo compound (3 equation 6). 1,2-Dithiins and their dibenzo derivatives have been prepared by oxidation of appropriate dithiols and related starting materials as outlined in equation (7). All of these reactions are, however, somewhat specialized and there has been essentially no systematic study of the preparation of six-membered heterocycles via formation of a bond between two heteroatoms. 

Dibenzo[l,2]dithiins are prepared by oxidation of appropriate dithiols and related starting materials, e.g. (40) - (41). 

An authoritative review covering application of UV photoelectron spectroscopy to heterocycles appeared in 1974 <74PMH(6)l) and important work on saturated multi oxygen and sulfur compounds is discussed therein. However, the studies of 1,4-dioxin, its dibenzo analogue, 1,4-dithiin and phenoxathiin, which are referred to in the first part of this section, appeared after the publication of that review. 

Desulfurization reactions in the 1,2-series are encountered among derivatives of both oxathiins and dithiins. 1,2-Oxathiin 2,2-dioxides extrude sulfur dioxide at elevated temperature over zinc oxide, iron or copper oxide to give the corresponding furan (66HC(21 -2)789) [cf. Section 2.26.3.1.2). Copper is a good catalyst for the extrusion of sulfur and sulfur dioxide from dibenzo[c,e3[l,2]dithiin (40) and its dioxide respectively to give dibenzothiophene (66HC(21-2)968). 

The reactivity of substituents has received little systematic study. However, with regard to electrophilic substitution reactions, it can be deduced from the products of monobenzo fused derivatives in the 1,4-series (Section 2.26.3.1.3) that the benzenoid ring is less reactive than the heteroring. The same conclusion applies to a phenyl group attached to 1,4-dithiin. In the dibenzo fused derivatives this type of competition is precluded and electrophilic attack occurs readily at the 2-position. The site of attack by a second incoming group is a little difficult to generalize upon and this is discussed in Section 2.26.3.2.2. Reactivity of the dibenzo fused compounds towards butyllithium has been well studied and proton abstraction occurs at C-l (or C-4 in phenoxathiin) (Section 2.26.3.2.3). 

Synthetically useful routes to dibenzo[c,e J[l,2]dithiins are normally based on cyclizations of biphenyI-2,2 -disulfonyl chlorides. A method applied successfully to the parent compound reduces the precursor with zinc in acetic acid to generate the bis thiol, which is then gently oxidized to the dithiin using iron(II) chloride (66HC(21-2)952). An alternative one-step reductive cyclization, which has been applied to the preparation of the 2,9- and 3,8-dinitro derivatives, involves reduction of the appropriate bis sulfonyl chlorides with hydriodic acid in acetic acid (68MI22600). Yet another reductive cyclization uses sodium sulfite followed by acidification, and these conditions lead to dibenzo[c,e][1,2]dithiin 5,5-dioxide. The first step of the reaction is reduction to the disodium salt of biphenyl-2,2 -disulfinic acid which, on acidification, forms the anhydride, i.e. dibenzo[c,e][l,2]dithiin 5,5,6-trioxide. This is not isolated, but is reduced by the medium to the 5,5-dioxide (77JOC3265). Derivatives of dibenzo[c,e] [1,2]dithiin in oxidation states other than those mentioned here are obtainable by appropriate oxidation or reduction reactions (see Section 2.26.3.1.4). 

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