Thieno dithiin

A thiophene ring can also be produced from two methylene groups. Here 2,5-dicarbethoxy-3,4-dicyanomethylthiophene 19 reacted with sulfur mono-chloride to give tetrasubstituted thieno[3,4-c]thiophene 20 in moderate yield (2002JCX72453). A mechanism for the thiophene 20 formation was proposed and 1,2-dithiine derivative 21 was likely to be an intermediate (Scheme 10) because sulfur monochloride gave higher yields of 20 than SCl2. At the next step (21 20), sulfur monochloride apparently acted as an oxidant. 

Thieno[3,4-3]thiophenes 500 were prepared from thiophen-3-yl-substituted [l,3]dithiol-2-ones 496 in good yields <2003JOG7115>. The photochemical irradiation of 496 leads to thieno[3,4-f]dithiines 497 via a unique ring cleavage reaction and subsequent reductive treatment of dithiines 497 proceeds to give 2,3-dihydrothieno[3,4-/ ]thiophenes 498 and 499. Heating of 499 in the presence of further iodomethane leads to the formation of the thieno[3,4-/ ]-thiophenes 500 (Scheme 63). 

Thieno[2,3-r 1-l,2,3-thiadiazoles 40a-f heated with CS2 in a double compartment autoclave produced thieno[2,3-rfl-l,3-dithiol-2-thiones 41a-f <2001MOL145>. In addition to the thermolysis product 41e, thieno[2,3- / -l,2,3-thia-diazoles 40e also produced bisthieno[2,3-/ 2, 3 -< ][l,4]dithiine 42 in 36% yield (Equation 3). 

Few examples of photochemical transformations of the 10n heterocycles in this series have been reported. Notable is the conversion of thieno[2,3-c]isothiazoles (33) to thiophenes (37) by homolytic cleavage of the nitrogen-sulfur bond (Scheme 4). The enedithione (34) which arises from the initial diradical may undergo (a) cyclization via the bicyclic thiirane (35) or (b) electrocyclization to the 1,2-dithiine (36) <88H(27)2539>. Since similar rearrangements do not occur with isothiazoles, benzoisothiazoles, or the isomeric thieno[3,2-d]isothiazoles, this unique transformation is a direct consequence of the thieno[2,3-c]annelation. However, substituent effects on the efficiency of the transformation have not been explored. 

Thieno-l,4-dithiins (380) have been obtained (ca. 40% yield) from the diynes (379) (Scheme 30) <8300056,87MI707-02). Thieno-l,4-dithiins (382) and (383) have also been obtained from 4-bromo-3-chloro-2-sulfolene (381) and the sodium salt of ethane-1,3-dithiol (Equation (122)). These products are oxidized by peracetic acid to yield the further S-oxides <89CC1020,92CB499). 

From sulfur- and nitrogen-containing five-membered heterocyclic compounds Photocyclization of l,3-dithiole-2-ones 723 affords thieno[3,2-r ]dithiins 725. The reaction probably involves cycliza-tion of the intermediate dithiones 724 (Scheme 110) <20010L3573, 2003JOC7115>. 

The reaction of Q -cyano-/3-chlorocinnamonitrile 64 with KSCN, ROH, and active bromomethylene compounds (BrCH2X) gave the thieno[2,3-d]pyrimidine derivatives 65 [89EGP(D)273441]. Condensation of tetracyano-l,4-dithiin 66 with NaCN in THF produced 4,5,6-tricyano-thieno[2,3-d]pyrimidine-2-thiolate 67 (80JOC5113). 

W. Schroth, E. Hintzsche, H. Jordan, T. Jende, R. Spitzner and I. Thondorf, 1,2-Dithiins and precursors. 17. Synthesis and properties of thieno annellated 1,2-dithiins - structural influence on color. Tetrahedron, S3, 7509-7528... 

Example 3 Oxidative Polymerization of 9-(5,7-Di(thiophen-2-yl)- l,3I-dithiolo 4,5-b)thieno 3,4-e) l,4)dithiin-2-ylidene)-2,5,7-trinitro-9H-fluorene-4-carboxylic Acid (Trietbylene Glycol Monometbyl Etber) Ester (9) to give P7a ... 

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