Thiophen 2-ethynyl

The reaction of sulphides 59 bearing an ethynyl or a carbomethoxy group a to sulphur with f-butyl hypochlorite in methanol or ethanol gives high yields of the corresponding a-alkoxy sulphides (60) rather than sulphoxides (equation 29). Oxidation of benzo[b]thiophene with t-butyl hypochlorite in t-butyl alcohol at 30-40° gave the corresponding 2-chloro-l-benzothiophen-l-oxide 61 in 45% yield (equation 30). 

More recently, dithienylethenes 64 containing the (4-pyridyl)ethyl and (4-pyridyl)ethynyl groups at position 2 of the thiophene ring (080L2051) have been synthesized in a similar way. Photochrome 65 was prepared from 2-hydroxymethylbenzo[b]thiophene according to Scheme 19 (05IZV2697). 

An alternate approach to the palladium catalyzed ethynylation of thiophene derivatives has been reported by Zeni and co-workers. They coupled 2-(butyltelluro)thiophenes with different acetylenes (6.48.), The reaction, which was effectively catalyzed by palladium dichloride, was run in the absence of copper salts. The choice of base (triethylamine) and solvent (methanol) were both crucial for the success of the coupling.70... 

Neighbouring chloro and ethynyl functions are converted into a thiophene ring by either sodium sulphide-DMF or morpholine and sulphur. 

Terthiophene- fullerene dyad 2.106 (Chart 1.21), in which the fullerene unit was attached to the -position of the central thiophene unit through a rigid ethynyl spacer, was prepared by Komatsu et al. [207]. The synthesis was accomplished by lithiation of 3 -ethynylterthiophene [208] to generate the lithium acetylide, which subsequently was reacted with Ceo to form the ethynylated fullerenyl anion. By treatment of the latter with methyl iodide, dyad 2.106 was obtained in 35% yield. Another terthiophene-fullerene dyad... 

In an effort to overcome steric interactions due to -substituents in cyclotetra(2,3-thienylene)s 4.6 (see above), Marsella et al. synthesized expanded thiophene-fused didehydro [12]annulene 4.32, which incorporated two additional ethynylene groups between the -positions of the cycUc stmcture (Scheme 1.44) [408]. Regiospeciflc halogenation of a 2,2 -bithiophene and Sonogashira-type cross-coupling with the ethynylated counter part were key elements of the synthetic strategy, which was also used to prepare a further extended macrocycle 4.33 (Chart 1.54), profiting from quadrupolar interactions of the central phenylene units [409]. 

Similar reaction of a dimethylated thiophene yielded cyclotetramer 4.37, which is formed preferentially over the trimer in the cyciization of 3-ethynyl-4-iodo-2,5-dimethylthiophene (Scheme 1.47) [412],... 

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