Benzo thiophenes syntheses

Benzothiophenes have always been of interest for medicinal chemistry and can be found in a number of marketed drugs such as Sertaconazole (Gineder-mofix), Zileuton (Leutrol) and Raloxifene (Evista). The classical synthesis of benzo thiophenes starts from thiophenols, reacting with bromoacetaldehyde dimethyl acetal, followed by cycUzation using strong acid. An alternative and more convenient route was also described starting from benzaldehydes which... 

The first synthesis of the parent compound of the benzo[4,5]thieno[2,3-f]pyrrole ring system 387 <2003T1477> and its derivatives was accomplished using the same synthetic sequence (Scheme 42). Starting with 2-methyl-benzo[ ]thiophene-3-carbaldehyde 388, an intermediate 389 was obtained. Treatment of bromo compound 389 with sodium azide in ethanol led to the stable triazoline 390. 1,3-Dipolar cycloreversion of 390 was induced by a catalytic amount of />-TsOH to give the parent 2//-benzo[4,5]thieno[2,3-c]pyrrole 387. Alternatively, direct treatment of bromo compound 389 with excess ammonia furnished 387 in one step. Compound 387 was treated with di-/-butyl dicarbonate and 4-dimethylaminopyridine (DMAP) to give iV-BOC derivative 391. Reaction of 389 with... 

A Thorpe reaction scheme led to the synthesis of a benzo[( ]thiophene derivative (87) in 80% yield, when (86) was treated with sodamide in dry benzene (62JOC2821). While reactions are known to convert (87) into benzo[6]thiophene, this pathway has not yet been explored. 

This synthesis of benzo[6]thiophenes is probably the most widely exploited single method for such syntheses since its introduction about 1950 by a variety of workers. It is applicable to a great number of highly substituted benzo[6]thiophenes, and intermediates are generally readily available. In 1949 Werner (49RTC509) reported the synthesis of several 3-alkyl- and 2,3-dialkyl-benzo[( ]thiophenes by cyclodehydration of arylthioacetones (99) with phosphorus pentoxide or anhydrous zinc chloride. Arylthioacetaldehydes (99 R = H, R1=H, R2 = Me, Et or Ph) have been cyclized in 65-80% yields with phosphorus pentoxide. In 1950 Tilak (50PIA(A)(32)390) introduced the polyphosphoric acid-promoted cyclization of... 

In 1972 Wright79 prepared 3-chIorothieno[3,2- ]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[ ]-thiophene-2-carbonyl chloride derivatives.80-82 Methyl 3,5-dichloro-thieno[3,2- ]thiophene-2-carboxylate (95) and methyl 2-chloro-3-(5-chloro-2-thienyl)acrylate were also isolated. When the reaction was carried out in refluxing toluene or chlorobenzene, the acid chloride (94)... 

The synthesis of 1,2-benzodithiin has been achieved through cyclisation of the bisthiolate obtained from either phenylacetylene or benzo[ >]thiophene (95TL1421). These yellow solids are more stable than both 1,2-dithiins and can be oxidised at either sulfur atom and also under Swem conditions to give the 3-aldehyde. 

The synthesis of benzo[ >]thiophenes from o-nitrobenzaldehydes or o-nitrobenzonitriles and methyl thioglycollate can be viewed as an extension of the foregoing approach (Scheme 64) (72JOC3224). 

Thiophenes and their Benzo Derivatives (/ //) Synthesis and Applications... 

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