Samarium triisopropoxide

Miyanaga [2] prepared moderate molecular weight polyglycidol ethers, (II), by polymerizing the corresponding glycidol ether with samarium triisopropoxide, samarium tris(tetramethyl heptanedionate), and yttrium tris(tetramethyl hep-tanedionate) with methyl aluminoxane. 

The synthesis is initiated by the organocatalyzed cascade that activates a,p-unsaturated aldehyde 8 with the formation of an iminium ion (Scheme 14.2). In this way, the imidazolidinone catalyst allows hydride transfer from the Hantzsch dihydropyridine 9 onto the highly activated conjugated alkene 11, which creates the nucleophilic enamine intermediate 12. Because of the chirality of the organocatalyst, stereoselective Michael addition (97% ee) to the adjacent enone occurs, with minor preference for the cis diastereomer (2 1 dr). Fortunately, this undesired diastereomer slowly epimerizes to the required trans isomer, which produces (-l-)-ricciocarpin A when treated with samarium triisopropoxide. Besides the Cannizzaro-like redox disproportionation, which allows the lactone producing Evans-Tihchenko reaction to occur, samarium(III) also enhances the epimerization to the trans isomer and therefore produces the desired isomer in high selectivity. 

Both samarium iodide and ytterbium triisopropoxide catalyse the ring opening45 of epoxides by TMS-azide in the latter case, due to an acidic work-up, the products are isolated as vicinal azido alcohols. 

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