Thiophene 2.5- dihydro-2-carboxylic acid

Benzo[b]thiophene-2-carboxylic acid, 2,3-dihydro-synthesis, 4, 921... 

Thiophene-3-carboxylic acid, 4-acetoxy-2,5-dihydro-synthesis, 4, 927... 

The electrochemical reduction of thiophene-2-carboxylic acid to the 2,5-dihydro derivative (198) in 76% yield has been reported the tetrahydro derivative is obtained as a by-product in 15% yield (75IZV888). The reduction is carried out in 2M LiOH on Hg electrodes. 

Nishino et al. found that 2-acylthiophenes are also reduced to the corresponding 2,5-dihydro derivatives (equation 24) and the intermediate anions can be intercepted with alkylating agents (equation 25). The resulting compounds can be easily converted into the corresponding 1,3-dienyl ketones (equation 25). Dmitrienko and coworkers have found that the Birch reduction of thiophene-3-carboxylic acid leads to the 2,3-dihydro derivative. ... 

Sodium/ammonia" treatment also causes disruption of the ring in thiophene and simple thiophenes, however thiophene-2-carboxylic acid and 2-acyl-thiophenes can be converted into the 2,5-dihydro derivatives using lithium in ammonia, followed by protonation or trapping with an alkyl halide."" Side-chain reductions can be carried out with metal hydrides, which do not affect the ring. 

Benzo[Z>]thiophen 5-Oxides. - Mild methods for the oxidation of 2,3-dihydrobenzo[Z>] thiophens to the sulphoxide have been developed. The photochemical reactions of various 2- and 3-substituted benzo[ ]-thiophen 1-oxides led to different photodimers. From 3-chlorobenzo[b]-thiophen-2-carboxylic acid 1,1-dioxide, 1,3-oxazinones of biological interest were obtained through cyclization reactions with cyanamides and carbodi-imides. Secondary amines add to 2-phenylbenzo [b] thiophen 1,1-dioxide to give 3-amino-substituted 2,3-dihydro-2-phenylbenzo[b]thiophen 1,1-dioxides. " ... 

Di- and Tetra-hydrothiophens.—Birch reduction of thiophen-2-carboxylic acid with three equivalents of lithium in liquid ammonia gave 2,5-dihydrothiophen-2-carboxylic acid and several other products. When the Birch reduction was carried out with five equivalents of lithium and with methanol as the proton source, a single product, c/s-5-mercaptopent-3-enoic acid, was obtained. Birch reduction of t-butyl 5-t-butylthiophen-2-carboxylate gave the 2,5-dihydro-derivative upon treatment with zinc dust and trimethylchlorosilane and then quenching with molar sodium hydroxide, this gave a mixture of (123) and (124) in the proportions 1 8. ... 

Thien-2-yl)succinic anhydride was converted into 4-oxo-5,6-dihydro-4//-cyclopenta[h]thiophene-6-carboxylic acid 31 tmder Friedel-Crafts conditions (Scheme 33) [53]. 

C14 H22 02 S 2-cyclohexyl-5-ethyl-2,5-dihydro-thiophene-3-carboxylic acid methyl... 

Raney nickel reduction of 2-benzyl-5-ethylselenophene (71) yields 1-phenylheptane (72), a conversion analogous to the much used reductive desulfurization of thiophenes (73JGU871). The electrochemical reduction of selenophene-2-carboxylic acid gives a mixture of dimeric products the major product is compound (73). This is in contrast to the 2,5-dihydro derivatives obtained by electrochemical reduction of thiophene and furan carboxylic acids (82CS( 19)95). Wolff-Kishner reduction of 2-selenienyl 2 -thienyl ketone gives, in addition to the expected methylene derivative, 2-(pentenyl)thiophene (72ZOB1780). 

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