Pd-Catalyzed Fluoride-Free Cross Coupling of Alkenylsilanes and Germanes

5 Pd-Catalyzed Fluoride-Free Cross Coupling of Alkenylsilanes and Germanes 

The coupling reactions of alkenylsilanes generally require activation of the silicon due to the low reactivity of the C-Si bond. Introduction of heteroatoms on the 

The intrinsically activated alkenylgermanes 106 are more reactive in the cross coupling reaction (Fig. 39). The reaction is dependent on the palladium catalyst and, as a ligand, Pd(Pt-Bu3)2 works very efficiently in NMP to afford the desired coupling product 107 in better yield without the generation of the protonated byproducts, which generally cause poor yields in this type of coupling reaction. 

This coupling reaction of alkenylgermanes can be applied to the synthesis of estrogen receptor modulator tamoxifen (112), which is used in the clinical treatment of estrogen-dependent breast cancer (Fig. 40). The benzoyl triethylgermane (108) is olefinated with ynolate to give the aUcenylgermane 109, which is coupled 

---