Thiophene, 2,5-dichloro-, synthesis

Thiophene, 3,5-di-t-butyl-2-methyl-sulfonation, 4, 764 Thiophene, 2,4-dicarboxy-synthesis, 4, 870 Thiophene, 2,3-dichloro-synthesis, 4, 933 Thiophene, 2,5-dichloro-synthesis, 4, 933 Thiophene, 3,4-dichloro-... 

Benzo[b]thiophene-2-carboxylic acid, 3,4-dichloro-5-methoxy-synthesis, 4, 870... 

Dichlorothiophene can also be used for the synthesis of 3-substituted thiophenes, since it can be smoothly acylated and chloro-methylated in the 3-position, and the halogens can then be readily removed at the appropriate stage. 3-Thenylsuccinic acid (28) has thus been obtained by treating 2,6-dichloro-3-thenylsuccinic acid with sodium amalgam. 2-Bromo-3-thenylbromide can be utilized in a similar way. ... 

The synthesis of cycloproparenes resulting from formal fusion of a cyclopropene to furan and thiophene has been attempted with limited success. Reaction of the dichloro-oxabicyclohexane 180 (X = O) " afforded a cyclopropene 181 which ring-opened to a vinylcatbene 182, but the cycloproparene 183 was not produced. Similarly, the thia-analogue 180 (X = S) could not be converted to 184. The intermediate cyclopropenes and/or vinylcarbenes have been trapped. A cyclopropathiophene derivative 186 was generated, however, from 185. Although it was not isolable, it afforded a bis-adduct 187 when it was produced in the presence of isobenzofuran (45)." ... 

In 1972 Wright prepared 3-chlorothieno[3,2-6]thiophene-2-carbonyl chloride (94) in 11-13% yield by heating 3-(2-thienyl)acrylic acid, thionyl chloride, and pyridine, a method of synthesis of benzo[6]-thiophene-2-carbonyl chloride derivatives. " Methyl 3,5-dichloro-thieno[3,2-6]thiophene-2-carboxylate (95) and methyl 2-chloro-3-(5-chloro-2-thienyl)acrylate were also isolated. When fte reaction was carried out in refluxing toluene or chlorobenzene, the acid chloride (94)... 

Methods of synthesis of 3-chloro- and 3,4-dichloro-thiophenes have usually involved tedious procedures in which tri- and tetra-chloro derivatives are dechlorinated by reductive or other methods. Gthanolic potassium hydroxide converted 2,3,4,5-tetrachlorothiophene into a 50 50 mixture of 2,4- and 3,4-dichlorothiophenes direct heating of the same tetrachloro substrate gave a mixture of 2,3- and 2,4-dichloro isomers (48JA1158). 3,4,5-Trichlorothiophene was readily prepared by the reaction of 1,1,2,3-tetrachloro-l,3-butadiene with sulfur (82JOU348). 

A concerted elimination-cyclization mechansim, involving a sulfenyl halide in a 1,3-butadiene-1-thio system, is the most probable mechanism for the formation of benzo[6 Jthiophenes from cinnamic acids or 4-aryl-2-butanones by treatment with thionyl chloride. The reactions shown in Scheme 5 have been carefully worked out, and the intermediates isolated (75JOC3037). The unique aspect of this synthesis is the reduction of the sulfinyl chloride (a) by thionyl chloride to form the sulfenyl chloride (b). The intermediate (b) was isolated and converted in pyridine to the 3-chlorobenzo[6]thiophene-2-carbonyl chloride in 36% yield (73TL125). The reaction is probably initiated by a sulfenyl ion attack on the aromatic ring, since it is promoted by electron-releasing groups para to the site of ring closure. For example, when X in (36) was N02, a 23% yield of (37), a mixture of 5-and 7-nitro derivatives, was obtained, but when X in (36) was OMe, a 54% yield of (37) was obtained, contaminated with some 3,4-dichloro-5-methoxybenzo[6]thiophene-2-carboxylic acid. 

A commercial synthesis of 2-bromothiophene was reported in the year 2014 (14PAT-2).The synthesis consists of oxidative bromination of thiophene with hydrogen bromide and hydrogen peroxide in dichloro-ethane at 40 °C. The method is amenable for large-scale production. Additionally, sequential one-pot syntheses of tri- and tetra-substituted thiophene and fluorescent push-pull thiophene acrylates involving (het)aryl dithioesters as thiocarbonyl precursors were reported (14MI-001). 

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