四ヨウ化チタンの還元力を活用する新規合成反応

Abstract

We have been interested in diastereoface-discrimination reactions using a variety of TiX4, and have found that differences in the reactivities of the tetrahalides can enable distinct reaction pathways through selection of an appropriate tetrahalide derivative to promote the specific reaction. Titanium tetraiodide is an excellent reagent for the reductive formation of enolate species form α-halo carbonyl or imino compounds, and the subsequent reactions with carbonyl compounds give aldol products in good yields. Regarding chemoselective reductions using titanium tetraiodide, α-dicarbonyl or α-imino carbonyl compounds were chemoselectively reduced with titanium tetraiodide to give α-hydroxy or α-amino carbonyl compounds, respectively, in good to excellent yields. Subsequent reactions with aldehydes or imines realize the selective formation of amino alcohol or diamine derivatives in good yields. Pinacol coupling of aromatic and α-halo-α, β-unsaturated aldehydes was efficiently promoted by titanium tetraiodide in propionitrile to give the 1, 2-diol derivatives with high dl-selectivities in high yields. Chemoselective deoxygenation of sulfoxides was also carried out successfully using TiI4 as a reducing agent to give sulfides in good to excellent yields