Thiophenols, thioether synthesis

In order to evaluate the catalytic properties of our SILCAs, we chose to test them on a classic and simple reaction. As our laboratory has a great interest in heteroatomic compounds especially sulfurs (Robert et al. 1996 Pees et al. 2001 Thomas et al. 2006), we chose a thioether synthesis, and benzyl phenyl thioether in particular (Harmand, 2009). Conversion rates of reaction between thiols and halides depend on reaction conditions which are in most cases not really environment friendly (extraction difficulties, catalysts loss and so on) To prepare SILCAs, three steps are necessary first the solubilization of IL in chloroform, then the addition of the alumina nanoparticules in the solution and finally the solvent removal evaporation. This method allows the obtention of a supporting material coated with a thin and uniform IL layer. We first compare the reaction between phenyl bromide and thiophenol in a basic aqueous solution in methylene chloride, with (table 4, entry 2-21) or without (table 4, entry 1) prepared SILCAs (Fig. 18). 

Sjwyer and coworkers have developed an efficient alternative UUmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SnAt reaction. Phenol, thiophenol, or aniline reacts v/ith an appropriate aryl halide, In the presence of KF-aliunina and 18-crovm-6 In acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thio ether as shovm In Eqs. 9.6 and 9.7. ... 

Thiophenols undergo base-catalyzed, Michael addition to acetylenic acids and esters to give trans addition products. These vinyl thioethers have been used in the synthesis of thiochromones. " Recently, Undheim and Lie have shown that thiophenol adds to DMAD with concomitant cyclization to give benzo[6]thiophenes. 

Thiation of aromatic compounds is utilized both for the preparation of aryl sulfides and for the generation of sulfur heteroarenes. The diaryl thioether motif is found in the structure of several approved pharmaceuticals, such as antihistamines. In a recent letter, Wu and He disclosed that Cu(I) catalysis is very efficient for the coupling of thiophenols with aryl iodides (Scheme 39) [ 108]. The procedure is very similiar to the diaryl ether synthesis under microwave irradiation reported by the same authors. 

Haloboranes will cleave MOM ethers in functionally dense substrates. Trichloro-borane without the nucleophilic assistance of thiol or thioether additives has been used457 and trifluoroborane etherate, in the presence of thiophenol, was used by Corey and co-workers in a synthesis of Ginkolide A45K and by Vedejs and Larsen to cleave a tertiary MOM ether in a synthesis of Fulvine and Cris-patine [Scheme 4.24b]459... 

Elimination of Benzylic Phenyl Thioethers. That C-S bond activation by CuOTf is not limited to substrates that can generate sulfur-stabilized carbocation intermediates is illustrated by a C-C connective synthesis of trans-stilbene (eq 56). The elimination of thiophenol under mild conditions is favored by benzylic stabilization of a carbocation intermediate or an E2 transition state with substantial carbocationic character. 

The synthesis of thioethers has been developed using various nickel-NHC complexes. The first report by Ying and coworkers [57] highlighted the abilitjr of a nickel catalyst to couple thiophenol with a variety of aryl bromides and iodides, producing high yields of diaryl thioethers. A recyclable nickel-NHC catalyst was also used in the formation of carbon-sulfur bonds, but was still restricted to the synthesis of diaryl thioethers [58]. Well-defined allyl nickel complexes were shown to be efficient for both the formation of carbon-sulfur and carbon-... 

Quaternary onium salts, crown ethers, and cryptates have all proved effective as catalysts in the synthesis of unsymmetrical thioethers under phase transfer conditions. Both primary and secondary alkyl bromides can be used to alkylate the mercaptan or thiophenol under basic conditions [5—9]. 

Synthesis ofEnol Thioethers. Using a Dean-Stark water separator, KIO catalyzes formation of alkyl- and arylthioalkenes from cyclic ketones and thiols or thiophenols, in refluxing toluene (eq 6). A similar catalysis is effected by KSF (in a faster reaction) and K1OF. The isomer distribution is under thermodynamic control. 

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