Copper arenethiolate chiral

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... 

Similarly, enantioselective conjugate addition of methyllithium and methylmagnesium iodide to benzylideneacetone is catalyzed by chiral copper(I) arenethiolates such as 2-[(/f)-l-(dimethyl-amino )ethyl]phenylthiolatocopper(I) with up to 57% ee68. 

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