Gallium lithium bis

Without question, the most significant advance in the use of sulfur-centered nucleophiles was made by Shibasaki, who discovered that 10 mol% of a novel gallium-lithium-bis(binaphthoxide) complex 5 could catalyze the addition of tert-butylthiol to various cyclic and acyclic meso-epoxides with excellent enantioselectiv-ities and in good yields (Scheme 7.11) [21], This work builds on Shibasaki s broader studies of heterobimetallic complexes, in which dual activation of both the electrophile and the nucleophile is invoked [22]. This method has been applied to an efficient asymmetric synthesis of the prostaglandin core through an oxidation/ elimination sequence (Scheme 7.12). 

The enantioselectivity was significantly influenced by the steric factor of the thiols employed. When p-MeC6H4SH and PhSH were used, the optical yields decreased to 69% and 3%, respectively. Shibasaki et al. have reported that gallium-lithium-bi-naphthoxide (GLB) 51 became a good catalyst for the enantioselective ring opening reaction of epoxide for the production of 52 (Eq. 7.39) [46]. 

Recently the first compounds containing Si=Ga or Si=In double bonds, l,3-disila-2-gallata- and -indataallenic anions respectively, were obtained in the form of lithium salts as dark red crystals by the reaction of bis(Ai tert butylmethylsilyl)dilithiosilane, with the respective M(III) halide (Figure 18). X-ray crystallographic analysis of gallium and indium salt derivatives showed that the >SiMSi< frameworks (M = Ga, In) are not linear and the two Si=M... 

Shibasaki developed the first catalytic enantioselective meso-epoxide ringopening reaction with 4-methoxyphenol (Scheme 2.15). ° This reaction was first found to be promoted by chiral gallium(m) lithium(i) bis(binaphtholate) (19), although the chemical yield was modest (31-75% yield) even with the... 

Scheme 2.15 Enantioselective meso-epoxide ring-opening reaction with 4-metbojgr-pbenol witb tbe use of chiral heterobimetallic gallium(m) lithium(i) bis[binaphtholate).

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