Thiophenes 3-hydroxy- from

Oxathiolium salts, anhydro-5-hydroxy-thiophene synthesis from, 4, 899... 

H- 1-Benzothiin, 3-bromo-4-hydroxy-3,4-dihydro-dehydration, 3, 908 2//-1-Benzothiin, 3,4-dibromo-thiophene synthesis from, 4, 902 277-1-Benzothiin, 3,4-dihydro-acylation, 3, 908 sulfilimines from, 3, 905 277-1-Benzothiin, 4-ethoxy-reactions... 

Shu C.K., Hagedorn M.L. and Ho C.T. (1986) Two novel thiophenes identified from the reaction between cysteine and 2,5-dimethyl-4-hydroxy-3(2//)-furanone. J. Agric. Food Chem. 34, 344-6. 

Thiophenes are formed by different reactions. The general reaction is that of furan derivatives with hydrogen sulfide (Figure 8.72). This mechanism is assumed, for example, in the formation of some thiophene derivatives from 4-hydroxy-2//-furan-3-ones. Alkylth-iophenes substituted in positions C-2 and C-3 may arise in reactions of 2-mercaptoethanal with unsaturated aldehydes, such as acrolein or but-2-enal (Figure 8.73). 2-Mercaptoethanal is a product of Strecker degradation of cysteine. 

Thiophene-2-carboxylic acid, 5-(dialkylamino)-thiophenes from, 4, 892 Thiophene-2-carboxylic acid, 3-hydroxy-synthesis, 4, 896... 

The reaction of diketosulfides with 1,2-dicarbonyl compounds other than glyoxal is often not efficient for the direct preparation of thiophenes. For example, the reaction of diketothiophene 24 and benzil or biacetyl reportedly gave only glycols as products. The elimination of water from the P-hydroxy ketones was not as efficient as in the case of the glyoxal series. Fortunately, the mixture of diastereomers of compounds 25 and 26 could be converted to their corresponding thiophenes by an additional dehydration step with thionyl chloride and pyridine. 

Thiophenes, from 4-hydroxythiazoies, 7 from 4-hydroxy-THISs, 5... 

Substituted 3-hydroxythiophenes are convenient starting-points for the synthesis of the thieno[3,2-Mthiophene system. Shvedov et obtained 50% of 3-chloro-3-ethoxycarbonyl-5-methylthiophene-2-aldehyde (110) from 3-ethoxycarbonyl-4-hydroxy-2-methylthiophene (109) by Vilsmeier formylation at 100°. Reaction with thioglycolic ter formed 3-ethoxycarbonyl-5-methoxycarbonyl-2-methylthieno[3,2-6]-thiophene (111) [. (36)]. 

The method has also proved to be applicable to the synthesis of polycyclic benzofurans naphthofurans from suitable naphthols,215 benzodifurans from Bz-hydroxybenzofurans,219 naphthodifurans from hydroxylated naphthofurans,228 thienobenzofurans from Bz-hydroxy-benzo[6]thiophenes.218,229... 

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