Thiophene derivatives

The vast majority of this class of compounds belongs to the benzo-thiophene-4,7-dione system (157), whereas compounds belonging to the benzothiophene-5,6-dione system are so far unknown. 

Oxidation of 3-phenyl-7-hydroxybenzothiophene with Fremy s salt afforded, in almost equal amounts, 3-phenyl derivatives of 156 and 157 (70MI3). Difficulties were encountered in the preparation of quinones from substituted alkyl benzothienyl-3-acetates. The only successful conversion of ethyl 6-hydroxy-5-methoxybenzothienyl-3-acetate was in a two-phase system with either aqueous periodate or thallate. The quinone was obtained in low yield (79JHC231). Some exteneded analogs could be prepared directly from the hydrocarbons with chromic acid (53CB366 56JCS3435). 

Much more work was done on extended quinones. Syntheses of six parent compounds (159-164) has been accomplished by two methods. In the first approach, a Friedel-Crafts reaction between thiophene-3,4-dicarboxylic acid and benzene or thiophenes was used, and in the second one chromium trioxide oxidation of the corresponding acetoxy derivatives was applied (72JOC1712). These systems behave differently in the presence of excess lithium aluminum hydride and aluminum hydride. Compounds 161 and 162 were reduced to hydroquinones, compounds 160 and 163 were deoxygenated 

Thiophene analogs of daunomycin (172, 173) were prepared in multistep reactions. The synthesis is based on a strong base-induced cycloaddition of homophthalic anhydrides. In the final step, glycosidation yielded a mixture of CL- and )S-glycosides from which the a-isomer was separated (87TL3971). 

The isomeric quinones 175, 176, and 177 were prepared from the corresponding dithiophene dialdehydes by a benzoin-type condensation and subsequent oxidation by air (69RTC1244). 

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Treatment of 192 with dimethyl acetylenedicarboxylate yields a thiophene derivative (195) when R = Ph and a 2-p3Tidone (1S>6) derivative when R = H (Scheme 100). The proposed mechanism involves the formation of a mesoionic derivative (193) initially further dipolar addition yields adduct 194, the decomposition of which is dependent on the R substituent as described for related compounds (435). ... 

THIOPHENE AND THIOPHENE DERIVATIVES] (Vol 24) Poly(thio-l,4-phenylene) [25212-74-2]... 

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