reaction mechanism

Silicon is a non-polar positive group without solitary electron pairs, so it is very stable in the reaction. This is incomparable with hydroxyl group, so the silicon group is often used as the substitution group of hydroxyl group in total synthesis. In addition, chiral alcohols can be obtained by asymmetric hydroxylsilication of olefins followed by Fleming-Tamao oxidation.

The first step of Fleming oxidation is the removal of phenyl, which converts stable phenylsilane into halogenated silane with relatively high activity by aryl electrophilic substitution.

Phenyl removal and oxidation should be carried out step by step, usually in one-pot synthesis. (I. Fleming, R. Henning, D. C. Parker, H. E. Plaut, P. E. J. Sanderson, J. Chem. Soc. Perkin Trans. 1, 1995, 317-337.). Phenyl can also be activated by adding bromine or other bromine sources to produce by-product bromobenzene.

Tamao oxidation uses more active fluorosilanes or chlorosilanes as substrates (RSiMenX (2-n)). Silicon, as a strong Lewis acid, exhibits more metallic properties in these substrates. In the reaction, a pentavalent intermediate, intermediate and hydrogen peroxide are formed by fluorination. The obtained intermediate is stabilized by hydrogen bond of fluorine and hydrogen, then rearranged and hydrolyzed to obtain the product:




The silane of rigid ring can also be oxidized by Tamao. The intermediate of fluorinated ring can enhance its Lewis acidity due to the relaxation of the tension of rigid ring.