Copper arenethiolate

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],...

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. 

Similar to the conjugate addition, the focus of the last decade has been put on the development of chiral copper catalysts for enantioselective S -substitutions of prochiral substrates.197,197a,197b 271,285 These represent a useful alternative for the preparation of those substitution products which cannot be obtained by anti-stereoselective copper-promoted or -catalyzed SN2 -substitution of chiral substrates (see Section 9.12.2.1.2). The first reported example for such a transformation is the reaction of the allyl acetate 333 with //-butylmagnesium bromide in the presence of 15 mol.% of the copper arenethiolate 334 which gave the substitution product 335 with exclusive y-selectivity and 50% ee (Equation (18)),286 286a... 

As these examples show, cyclic enones are normally used as substrates for copper-catalyzed enantioselective Michael additions. In some cases, however, good stereoselectivities were also attained with acyclic enones of type 11. Thus, van Klaveren, van Koten et al. [9] employed the copper arenethiolate 13 as catalyst for the 1,4-addition of methylmagnesium iodide to benzylideneacetone and obtained adduct 12 (R = = Me) with 76 % ee. Interestingly, this... 

A different strategy, involving chlorotrimethylsilane elimination from the reaction of a Zn or Cu halide with (frimethylsilyl)arenethiolates RSSiMes, has been described for the preparation of zinc- and copper arenethiolates (equation 22). 

C. Structures of Copper Arenethiolates with Intramolecular Coordination... 

The latter hexanuclear structural type [Fig. 20(b)] is different from the copper arenethiolate hexamers (Section II.C.5), since in these copper structures only n2-S bonded arenethiolate ligands are present, that is, the hexanuclear... 

In the area of mixed-arenethiolatocopper copper halide aggregates, there is still much exploration to be done since so far only two species are known. However, these species have structures that combine several features of both copper arenethiolates and copper halides and may therefore become interesting model compounds in the near future. 

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