Thioanhydrides, synthesis

An improved synthesis of dithieno[3,2-A2, 3 -<7]thiophene 15a has been achieved from 2,3-dibromothiophene 304 (Scheme 57). Lithiation of 2,3-dibromothiophene 304 using -butyllithium followed by oxidative coupling with cupric chloride provided 3,3 -dibromo-2,2 -bithiophene 305 in 79% yield. Treatment of 305 with 2 equiv of -butyllithium in ether at —78 °C under nitrogen for 40 min and then adding benzenesulfonic acid thioanhydride and leaving the reaction mixture to reach room temperature afforded dithieno[3,2-A2, 3 -<7]thiophene 15a in 70% yield <2002TL1553>. 

These methods parallel the synthesis just described for the five-membered rings. As indicated in structures (42)—(49), standard reactions of aliphatic chemistry can be extended to the preparation of piperidines, tetrahydropyrans and pentamethylene sulfides (44 Z = N, O, S) glutarimides, glutaric anhydrides and glutaric thioanhydrides (46 Z = N, O, S) and 8-lactams, 8-lactones and 8-thiolactones (49 Z = N, O, S). 

An attempt to scale up the synthesis of 2-thiophthalide by the reduction of phthalic anhydride with hydrogen sulfide gave 3,3 -bithiophthalide (106a), which arises by condensation of 2-thiophthalide (98) with phthalic thioanhydride (104) (Scheme III).118... 

The same approach was used for the synthesis of phenanthroE9,10-bl-thiophen. The bromination of naphthoE1 2-clthiophen with bromine in chloroform gave the expected 1,3-dibromo derivative, while NBS in acetic acid gave in addition a thiolactone and a thioanhydride. PhenanthroE9,10-c]thiophen reacted similarly with NBS in acetic acid. In acetone, only oxidation to the sulphoxide was obtained. 

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