Polycyclic thiophenes

Sometimes, hydrogen sulfide converts an oxygen-containing heterocycle into a sulfur-containing one, and as furans and polycyclic furans are very common in nature such reactions may be the origin of the polycyclic thiophenes mentioned above. A typical example is the formation of the isothiazolin-3-thione (6) from the isoxazolin-3-thione (7) on treatment with hydrogen sulfide and hydrogen bromide.8... 

A copper-mediated cyclization of metallated thiophenes has been utilized to prepare polycyclic thiophenes and thiophene cyclophanes. Treatment of dibromide 106 in succession with M-butyllithium (halogen-metal exchange), zinc chloride (transmetallation), and copper chloride gave 7//-cyclopcnta[ 1,2-fc 4,3-6 dithiophene (107) <00H(52)761>. This conversion has also been achieved using a palladium-mediated cyclization performed in the presence of hexamethylditin . Copper-mediated cyclizations have also been applied to the syntheses of cyclopenta[2,l-6 3,4-A ]dithiophen-4-one (108) (three steps from 73) <00S1253> and cyclophane 109 <00CC2329>. 

Polycyclic Thiophene Derivatives from Diels-Alder Reactions of Vinylthiophenes 908... 

Miscellaneous Carbocyclic Ring Closures to Form Polycyclic Thiophene Derivatives 908... 

This chapter will review synthetic methods for the preparation of thiophenes, benzothiophenes and polycyclic thiophenes. In addition, a survey of the applications of thiophenes and derivatives will supplement the specific discussion included in Chapters 1.04 through 1.16 of this work. 

The synthetic methods will be arranged in order of bond formation, beginning with the formation of one bond, between sulfur and carbon-2 of thiophene, and proceeding around the ring, then two bonds, etc. This method is outlined in the chapter by Meth-Cohn (B-79MI31500) who has calculated that there are 19 different ways that thiophenes can be formed by different bond formations. Of these only 11 are of practical value currently. We have treated benzothiophenes and other polycyclic thiophenes as derivatives of thiophene, and discussed their synthesis in the specific bond formation sections. Likewise since methods... 

By synthesizing bromoalkyl-sulfur and -oxygen based heterocycles, Lautens was able to extend the strategy to include the synthesis of polycyclic thiophenes and furans [83, 84], Under similar reaction conditions to those used for nitrogen-based heterocycles, polycyclic products were obtained in good to excellent yields (Scheme 35). The electronic nature of the aryl iodide had a large impact on the observed yields, as electron-deficient aryl iodides worked well, while little to no product was obtained with electron-rich ones. Based upon these results, Lautens proposed that the mechanism of direct arylation of thiophenes occurs through an electrophilic metalation mechanism. 

Polycyclic Thiophens. - Castle and coworkers are continuing their extensive work on the synthesis of polycyclic thiophens as possible constituents in coal. All of the monomethyl isomers of (332), (333) , and (334) have been prepared by photocyclization of 3- and 2-styrylbenzo[blthiophens. The pentacyclic thiophens (335) and (336) have been synthesized from 3-methylphenanthro-... 

Photocyclizations (new bonds indicated by arrows) represent an additional tactic in the synthesis of complex thiophenes. Synthesis of [7]heterohelicine 175 involved a double-photocyclization as a key step . Complex polycyclic thiophenes 176 and 177 were synthesized by the photolysis of the corresponding chlorothiophenes. 

The quinodimethane (642), generated by reaction of (640) with 2-benzo[i]thienyllithium (641), condenses with (641) to give the polycyclic thiophene (643) (Scheme 130) <94TL7597>. Intramolecular Horner reaction of (644) affords the polycyclic thiophene (645) (Equation (117)) <94CC1859>. Condensation of thiophenedialdehyde (6 ) with 1,4-dicarbonyl compounds leads to benzothiophenes... 

General.—Recent publications include a chapter on thiophens in a comprehensive treatise an article on recent advances in the synthesis of benzo[6]thiophens a published plenary lecture on condensed thiophens, especially thienothiophens, selenolothiophens, and related systems and a review on the synthesis of polycyclic thiophens from the direct insertion of heterosulphur bridges into vinylarenes, biaryls, and angularly condensed arenes, ... 

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