Arenethiols

Arenethiols. Most of the chemistry described for alkanethiols is not appHcable to ben2enethiols and other arenethiols. The synthesis of ben2enethiol is best carried out by reduction of the ben2ene sulfonyl chloride (eq. 17). Other methods for synthesi2ing arenethiols are discussed at greater length in the Hterature (28). 

Scheme 3.14 Bis(arenethiolates) zinc complexes for addition of ZnEt2 to benzaldehyde.

Autoclave reactions involving ethylene oxide with alkanethiols or an (unspecified) alcohol went out of control and exploded violently. Similar previous reactions had been uneventful [1], An arenethiol was being reacted with ethylene oxide under catalysis by a fraction of a percent of sodium hydroxide (solid) dissolved in the thiol to which the oxirane was slowly charged. After an initial exotherm a white solid precipitated, the exotherm died away and later resumed, with dissolution of the solid, the reaction then running out of control from the backlog of charged oxirane [2],... 

Several Pd11 complexes with thiolate or thioether derivative ligands have been studied to be applied in the hydroxycarbonylation reaction.394 Aminothiolate complexes of palladium with PPh3 catalyze the conversion of styrene to 2-phenylpropionic acid in high yield and excellent regioselectivity.644 Under mild conditions and in the presence of a catalytic amount of an S, TV-chelated palladium or//zo-amino-arenethiolate complex, styrene reacts with CO and oxalic acid or water to selectively give 2-phenylpropanic aid in high yield.645... 

Other examples are provided by structures with bridging arenethiolate anions. The application of functionally substituted copper arenethiolates as catalysts in... 

Scheme 3.47. Copper arenethiolate-catalyzed conjugate additions of methyllithium to enynoates [194],...

The copper)I) arenethiolate complexes 19 [30], first developed and studied by van Koteris group, can be used as catalysts for a number of copper-mediated reactions such as 1,4-addition reactions to enones [31] and 1,6-addition reactions to enynes [32]. 

Initial studies on the application of these catalysts to allylic substitution reactions showed that the arenethiolate moiety functions as an excellent nontransferable group, and that the regioselectivity can be completely reversed by suitable changes in the reaction parameters [33]. If the reaction between geranyl acetate and n-BuM gl was carried out inTHFat—30°C with fast addition of the Grignard reagent to the reaction mixture, complete a selectivity was obtained. Raising the tempera-... 

To investigate the effect of the substituents in the arenethiolate structure, four differently substituted copper arenethiolates, 25-28, were tested as catalysts, but very low ees were obtained in all cases [34]. The oxazolidine complex 26, developed by Pfaltz et al. [36] and used successfully in asymmetric conjugate addition reactions to cyclic enones, gave a completely racemic product with allylic substrate 20a. 

To avoid the difficulties in handling the highly air-sensitive copper arenethiolates, a method for their preparation and utilization in situ has been developed, the aren-ethiol 29 being deprotonated with n-BuLi and mixed with a copper(l) salt to yield the active catalyst [34]. 

Use of this technique results in an equivalent of lithium halide being present in the reaction mixture, unlike when the isolated copper arenethiolates are employed. Lithium salts can have very profound effects on copper-mediated reactions, but in this case a similar ee (40%) and complete y selectivity were still obtained for the reaction between 21 and n-BuMgl when the catalyst was prepared from Cut. Nei-... 

The moderate ees obtained with the copper arenethiolate ligands discussed above prompted a search for new chiral ligands for use in asymmetric allylic substitution reactions. The binaphthol-derived phosphoramidite ligand 32, used successfully by Feringa et al. in copper-catalyzed 1,4-addition reactions [37], was accordingly tested in the reaction between 21 and n-BuMgl. 

Chiral ferrocenes have received much attention as ligands in metal-catalyzed reactions [39], but their use in copper chemistry has been very limited [40, 41]. The ferrocene moiety offers the possibility of utilizing both central and planar chirality in the ligand. By analogy with the copper arenethiolates described above, ferrocenyl copper complex 33 (Scheme 8.20) is extremely interesting. 

Yu and coworkers reported the design and synthesis of a series of conductive OPEs possessing a ferrocene and thiol at each terminus [101]. The solubility is achieved by substitution at the phenyl groups with methyl and propoxy substituents (67). Several new reactions for preparing novel arenethiol-protected compounds (e.g., 2-(4-pyridinyl)ethyl-4 -(ethyl)phenyl sulfide) are reported. 

---