Thiophene from dione

A solution of 2 grams of A -19-norandrosten-3,17-dione and 0.4 gram of pyridine hydrochloride in 50 cc of benzene free of thiophene was made free of moisture by distilling a small portion 4 cc of absolute alcohol and 4 cc of ethyl orthoformate were added and the mixture was refluxed during 3 hours. 5 cc of the mixture were then distilled and after adding an additional 4 cc of ethyl orthoformate the refluxing was continued for 2 hours longer. The mixture was evaporated to dryness under vacuum and the residue was taken up in ether, washed, dried and evaporated to dryness. The residue was crystallized from... 

Examples of reactions involving replacement and cyclization are the long-known preparation of thiophenes (89) from 1,4-diketones, and the formation of l,2-dithiole-3-thione (90) from the salicylate ester analog (91).120 In the latter instance, oxidative cyclization with formation of an S—S bond has occurred this is a common feature of these reactions, particularly if such a link is needed to complete a five-membered ring. Another example of this aspect is afforded by the reaction of the propane-1,3-dione derivatives (92) which yield 3,5-diaryl-1,2-dithiolylium salts (93) when heated with phosphorus pentasulfide in carbon disulfide, followed by perchloric acid.121... 

The preparation of norbomadiene-fused thiophene (17) involved a double-Wittig reaction of 1,2-dione 15 with the bis-ylide derived from phosphonium salt 16 <99BCSJ1597>. The effect of the fused heteroaromatic ring of 17 (neighboring group participation) on electrophilic substitution of the norbomadiene ring was examined. 

An example of transfer of electron from nucleophile to substrate is seen in the formation of the radical anions (observable by ESR) of 5-halo-2A/,3W-benzotf>]thiophene-2,3-diones on treatment with nucleophiles.20 It has been proposed in some cases, that this single-electron transfer step takes place through a charge transfer complex between the nucleophile and the aromatic substrate.21-22 Some reactions occur spontaneously, i.e. without any catalysts or reagents other than the substrate and the nucleophile, but the initiation process is usually, although not invariably, photostimulated (near-ultraviolet radiation, 300-... 

Ketyls from dicarbonyl compounds in the thiophene series have also been examined. The Bologna group has studied the conformational equilibria in the anion-radical of thiophene-2,5-dicarbaldehyde. They have also investigated the intramolecular cation exchange process within ion-pairs of this ketyl, and of analogous ketyls from the isomeric thienothiophenes, and the consequence for this process of variation in the size of the cation and its complexation by macrocyclic polyethers. The anion-radicals of the isomeric l,2-dithienylethane-l,2-diones (thenils) were recorded several years ago. " ... 

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